Organic, Hybrid, and Perovskite Photovoltaics XXV

This talk will consider the future of metal halide perovskite (MHP) photovoltaic (PV) technologies as photovoltaic deployment reaches the terawatt scale. The requirements for significantly increasing PV deployment beyond current rates and what the implications are for technologies attempting to meet this challenge will be addressed. In particular how issues of CO2 impacts and sustainability inform near and longer-term research development and deployment goals for MHP enabled PV will be discussed. To facilitate this, an overview of current state of the art results for MHP based single junction, and multi-junctions in all-perovskite or hybrid configurations with other PV technologies will be presented. This will also include examination of performance of MHP-PVs along both efficiency and reliability axes for not only cells but also modules placed in context of the success of technologies that are currently widely deployed.

The recent advent of robust, refractory (having a high melting point and chemical stability at temperatures above 2000°C) photonic materials such as plasmonic ceramics, specifically, transition metal nitrides (TMNs), MXenes and transparent conducting oxides (TCOs) is currently driving the development of durable, compact, chip-compatible devices for sustainable energy, harsh-environment sensing, defense and intelligence, information technology, aerospace, chemical and oil & gas industries. These materials offer high-temperature and chemical stability, great tailorability of their optical properties, strong plasmonic behavior, optical nonlinearities, and high photothermal conversion efficiencies. This lecture will discuss advanced machine-learning-assisted photonic designs, materials optimization, and fabrication approaches for the development of efficient thermophotovoltaic (TPV) systems, lightsail spacecrafts, and high-T sensors utilizing TMN metasurfaces. We also explore the potential of TMNs (titanium nitride, zirconium nitride) and TCOs for switchable photonics, high-harmonic-based XUV generation, refractory metasurfaces for energy conversion, high-power applications, photodynamic therapy and photochemistry/photocatalysis. The development of environmentally-friendly, large-scale fabrication techniques will be discussed, and the emphasis will be put on novel machine-learning-driven design frameworks that leverage the emerging quantum solvers for meta-device optimization and bridge the areas of materials engineering, photonic design, and quantum technologies.

The organic solar cells have experienced a great improvement in efficiencies over the past 5 years, mostly due to the development of new acceptor materials including the landmark acceptor, Y6, and a series of Y6-based derivative acceptors. In this work, we study a broad range of Y6-type acceptors using transient optical spectroscopy techniques and reveal the precise relationships between molecular structure, film morphology and ultrafast excited-state dynamics in these materials, which are closely correlated to the corresponding blend device performance.

Organic solar cells (OSCs) have the potential to be the next generation solution for green energy after the silicon solar cells. However, one challenge that lies in front of the OSCs is the inadequate photostability. So far, one mystery to unravel is the mechanism of degradation in the carrier transport interface during the OSC photoaging. In our work, we demonstrate that the damaged hole-transport layer—molybdenum oxide (MoOx) is the main reason for photo-degradation. The power conversion efficiency (PCE) of encapsulated OSCs dropped to 50% of their original value after 100 hours of photoaging under 1 sun intensity, AM1.5 G irradiation provided by a 1000 W Xenon solar simulator. In contrast, adding a protective buffer layer between the MoOx and the photoactive bulk heterojunction (BHJ) layer in the same devices significantly improved the photostability of OSCs. With the buffer layer, the PCE of OSCs maintained 80% of their original value after 100 hours of photoaging.

2D perovskites solve the instability issue of 3D perovskites, but show lower efficiency due to random quantum-well structures. Our aim is to tune the phase distribution in formamidinium (FA)-based quasi-2D perovskites (< n>=5) with multiple microstructural domains of different n values. Dion-Jacobson spacer 1,4-phenylenedimathanammonium (PDMA) and Ruddlesden-Popper spacer propylammonium (PA) are mixed to regulate the phase distribution into a normal gradient, namely 3D domain on top and 2D domains (n=2-6) on the bottom. A moderate methylammonium (MA) incorporation stabilizes the perovskite structure and also fine-tunes the bandgap.

Perovskite solar cells (PSCs) have rapidly improved in efficiency, yet face challenges hindering commercial competitiveness. Enhancing thin film homogeneity and grain size while addressing stability is crucial. Methyl ammonium lead iodide (MAPbI3) limitations have spurred interest in formamidinium lead iodide (FAPbI3) for stability and efficiency. However, FAPbI3 phase degradation hampers long-term stability. Our previous work demonstrated improved stability via aerosol-assisted crystallization. Here, we refine this method by adding methylammonium thiocyanate (MASCN) to enhance film crystallinity and grain size. This additive approach prolongs charge-carrier lifetimes, enhances stability, and boosts device efficiencies, expanding processing options for enhanced perovskite performance.

In this work, we demonstrated a fluorescence lifetime imager for real-time measurement of a microfluidic synthesis platform. We were able to observe changes in fluorescence lifetime induced by different reaction parameters during the synthesis process. Fluorescence lifetime data also provided information on the optical properties of perovskite nanocrystals (PLQY, shape, size, and spectrum). Since the fluorescence lifetime is determined by the spatial arrangement of nanocrystals, synthesis parameters, fluorescence intermittency, etc., our study utilized fluorescence lifetime as a real-time indicator for the flow synthesis conditions. Our custom-built fluorescence lifetime system can measure luminescence lifetime at a wide time range (0.1ns ~ 5μs). This system provides information on the physical, chemical, and photophysical properties of various perovskite nanocrystals and other luminescent materials.

Investigation on Electronic Structure and Optical properties of lead free double perovskite A2SnCl6 (A= Sr, K) From First Principle Study P.Pavankumarreddy, 1R. Mahesh, 1Anandpandarinath,AksharaPerumalla,Kandula Ruchithareddy 1Dept.of Physics, Vidya Jyothi Institute of Technology The double perovskite materials A2SnCl6 (A= Sr, K) demonstrate significantly enhanced stability compared to Sn2+ based perovskites, as well as promising optoelectronic properties including direct bandgaps. A2SnCl6 adopts a vacancy-ordered double perovskite structure featuring isolated [SnCl6] octahedra, which contribute to a quantum confinement effect that enhances photoluminescence. The calculated structures exhibit a cubic phase with the Fm-3m space group, and their lattice parameters agree closely with reported values. All double perovskites exhibit mechanical stability. The band gaps of the perovskites vary depending on the A substitution from K to Sr. The total density and partial density of states provide insights into the variations in band gaps. The optical properties are determined through frequency-dependent dielectric functions, with optical absorption occurring in the visible range of 400-800nm

This study investigates the potential commercialization of inverted organic solar cells due to their enhanced stability, despite lower efficiencies compared to traditional designs. Using PTQ10:BTP-eC9 and PM6:BTP-eC9, the research reveals that the distinct vertical distribution of the active layer impacts device performance. PTQ10:BTP-eC9 exhibits efficiency differences between conventional (15.35%) and inverted (12.53%) structures due to its unique distribution. Introducing PC71BM mitigates this issue, resulting in negligible efficiency differences (13.70% for inverted and 14.17% for conventional devices), providing valuable insights for improving the performance of inverted organic solar cells for practical applications

Cs_2 TiI_6 shows promise for lead-free perovskite solar cells (PSCs), boasting favorable optoelectronic properties. Investigating crystal structure, optical behavior, and electronic characteristics, Cs_2 TiI_6 proves a strong candidate for photovoltaic (PV) applications. Six PSC configurations, integrating Cs_2 TiI_6 as the absorber layer and WS_2, PCBM, TiO_2, Cu_2 O or Spiro-OMETAD as charge transport layers, were analyzed. The optimal setup, ITO/TiO_2 / Cs_2 TiI_6/Cu_2 O/Au, achieves 22.71% efficiency, 87.88% fill factor, 1.442V open-circuit voltage, and 17.92 mA/cm^2 short-circuit current density. This study advances lead-free PSCs, highlighting Cs_2 TiI_6's potential in sustainable energy solutions, fostering innovation in renewable energy.

A fill factor (FF) in polymer solar cells has been least studied but should be deeply understood in the photovoltaic parameters. An empirical equation for FF shows FF is related to not only the photovoltaic parameters but also device parameters. However, FF in polymer solar cells cannot be explained by the empirical equation with such parameters. Rather, it is significantly dependent on charge carrier dynamics in polymer solar cells. In this study, we first discuss how FF can be explained by using an empirical equation for FF based on the equivalent circuit model. Next, we discuss the limiting factors of FF in terms of charge carrier dynamics, which were evaluated by transient optoelectronic measurements. We propose that for high FF to be achieved in polymer solar cells, it is essential that the mobility of the fast component exceed ~10−3 cm2 V−1

Recent research underscores sputter-deposited nickel oxide (NiOx) films' importance in perovskite solar cells. Deposition conditions and post-treatment influence NiOx/perovskite interface, vital for efficient charge transfer. This study delves into the characterization of a NiOx film deposited on top of indium tin oxide (ITO) covered substrates using the magnetron sputtering technique. Thickness variations, thermal treatments, and chemical modification of the surface are investigated to achieve optimal transparency, adhesion and interface morphology, aiming for device performance improvements. UV-vis spectral characterization, Secondary Ion Mass Spectrometry Time of Flight (SIMS TOF), Scanning Electron Microscopy (SEM), and Atomic Force Microscopy (AFM) measurements were carried out to evaluate the impact of deposition and post-processing conditions. An inverted solar cell with the structure ITO/ NiOx/ MAPbI3/ ZnO/ Ag, using optimized sputter deposition of NiOx as the hole transport layer and ZnO as the electron transport layer, was fabricated and characterized.

This investigation assesses the effect of different encapsulation materials and environmental conditions on ionic currents in methylammonium lead iodide (MAPI) thin films, which are essential for the stability of perovskite solar cells. Encapsulation types such as PMMA, MgF2, and SiO2 were examined under both air and vacuum conditions, complemented by an epoxy-sealed glass cover for extra protection. Employing the photo-electromotive force technique to analyze ion dynamics, findings indicate that environmental exposure and layer interaction profoundly influence ionic activity. While a single encapsulation layer falls short in protecting against environmental factors, combining SiO2 with an epoxy-sealed glass significantly improves MAPI film stability, albeit the epoxy layer alters ionic responses, underscoring the complexity in optimizing encapsulation for enhanced solar cell performance.

Aerosol-Assisted Solvent Treatment (AAST) is an effective post-treatment method designed to improve the grain size of perovskite films, thereby reducing grain boundaries (GBs) and improving the performance of solar cells. During the application of AAST on perovskite films deposited on flexible substrates, a red shift in Photoluminescence (PL) was observed. Combined with X-Ray Diffraction (XRD) analysis, this phenomenon was attributed to the in-plane compressive stress within the grain boundary of perovskite. To address this issue, the process was adapted by simply bending the perovskite film during AAST, effectively reducing the aforementioned stress. This modification maintained the balance of strain engineering, offering a nuanced approach to optimizing the treatment process for flexible substrates.

Self-assembled monolayers (SAMs) have emerged as promising hole transport layers (HTLs) in organic solar cells (OSCs). The compound 2PACz has demonstrated superior performance compared to the conventional PEDOT: PSS. The latter is known to have poor stability and can also suffer from weak interfacial adhesion energies, leading to delamination failures within the device stack. Our investigation is focused on the impact of SAMS on OSC performance, operational stability, and mechanical stability. We hypothesize that halogenation of 2PACz will enhance adhesion strength through electrostatic bonding. We have conducted a comparative analysis of a number of SAMs including Cl-2PACz, Br-2PACz, and MeO-2PACz. We explore their impact on adhesion through peel tests and DCB tests. We show that the use of 2PACz results in a threefold increase in peeling strength relative to PEDOT: PSS. Additionally, our OSCs exhibited nearly a 1% increase in PCE with Br-2PACz.

In this work, we report a lead-free MASnI3 perovskite photodetectors prepared by inverse temperature crystallization method. The surfaces of MASnI3 perovskite films are smooth and evenness. The MASnI3 perovskite photodetectors t has the highest photocurrent value in green light region among the five monochromatic light sources with a photocurrent of 1 uA at bias of 10 V. The advantage of this work is that the manufacturing process is relatively simple and safety, so it can be easily manufactured.

This study explores the use of elastomer additives to increase the mechanical reliability of flexible organic solar cells (OSCs) with minimal impact on device performance. In particular, we compare the addition of styrene-ethylene-butylene-styrene (SEBS) and styrene-ethylene-propylene-styrene (SEPS) co-polymers with varying polystyrene content and molecular weight. Our findings reveal that SEPS exhibits slightly higher miscibility than SEBS. Yet, the miscibility difference is relatively small, and casting conditions that drive local morphology become a larger driver dictating final device performance. In both the SEBS and SEPS additives, we can maintain 95% of the control OSC efficiency. This is achieved while significantly improving the fracture toughness of the OSCs. The fracture energy is shown to be strongly driven by the molecular weight of the additive, and optimized elastomer additives can result in a more than a four-fold increase in OSC fracture toughness.

In this contribution, the atomic layer deposition technique is proposed to deposit zinc–tin-oxide as a buffer layer in Ag-doped CZTSSe solar cells. The zinc–tin-oxide buffer layer improves the band alignment at the Ag-CZTSSe/ zinc–tin-oxide heterojunction interface. The smaller contact potential difference of the zinc–tin-oxide facilitates the extraction of charge carriers and promotes carrier transport. The better p–n junction quality helps to improve the open-circuit voltage (Voc) and fill factor (FF) and the final device delivers a higher efficiency of 11.8%. On the other hand, organic solar cells (OSCs) have gained much attention in the past few years. The efficiency of OSCs has been significantly improved, however, stability is still a big challenge. Herein, we introduced a polymer-based additive strategy to improve the efficiency and stability of inverted non-fullerene organic solar cells based on ZnO as a cathode interfacial layer. The device with polymer-based additive improved the efficiency and stability maintaining more than 90% PCE after storage in a nitrogen-filled glove box for one month.

Perhaps the single most important problem confronting the development of OLED displays and lighting today is how to achieve sufficiently long triplet-controlled emission device lifetime to prevent rapid color change during operation, while achieving 100% internal emission efficiency. It has been shown1 that bimolecular (e.g. triplet-polaron, triplet-triplet) annihilation provides a source of energy sufficient to destroy the blue triplet chromophore (whether a phosphor or a TADF molecule) or its host. Since that time, many materials, structures and strategies to extend blue emission lifetime based on this understanding have been demonstrated. Furthermore, various molecular fragments have been identified whose presence leads to the observed luminance loss. Unfortunately, a fully satisfactory solution has not been shown where blue triplet emitter lifetime is sufficient to meet the standards of high performance displays, although white OLED illumination sources may now have adequate lifetime to meet industry standards. In this talk I will discuss progress in extending blue phosphorescent OLED (PHOLED) lifetime, and in understanding of the limitations to extending the lifetime of blue triplet emitters. In particular, I will focus on the relationship between radiative state lifetime, exciton density, and the longevity of the PHOLED. I will review efforts that have resulted in increasing the deep blue phosphorescent longevity by at least 14 X via emitter design, polaritons, and optical cavity engineering. Prospects for future advances will be discussed. 1. “Intrinsic luminance loss in phosphorescent small-molecule organic light emitting devices due to bimolecular annihilation reactions”. N.C. Giebink, B.W. D’Andrade, M.S. Weaver, P.B. Mackenzie, J.J. Brown, M.E. Thompson, and S.R. Forrest, J. Appl. Phys., 103, 044509 (2008).

Commercial carbazole (Cz) has been widely used to synthesize organic functional materials, which are entwined with recent breakthroughs in ultralong organic phosphorescence, thermally activated delayed fluorescence, organic luminescent radicals, and organic semiconductor lasers. Recently, we discovered that different from commercial Cz, the fluorescence of lab-synthesized-Cz (Lab-Cz) is blue-shifted by 54 nm and the well-known room-temperature ultralong phosphorescence almost disappears. Detailed studies reveal the presence of a Cz isomer as the impurity, which is widespread in commercial Cz sources with <0.5 mol%. Ten representative Cz derivatives were resynthesized from the Lab-Cz and all failed to show the reported ultralong phosphorescence in the same crystal states. However, even 0.1 mol% isomer doping can recover the reported ultralong phosphorescence. The presence of the isomer in commercial carbazole triggers us to re-examine the structure-property of many optically active materials with important discoveries.

Fluorescence-based sensing has the potential for sensitive (trace), rapid and selective detection of chemical threats and is compatible with low power portable detectors that can be used in the field by military personnel, first responders, healthcare workers and those tasked with environmental monitoring. Chemical threats can include illicit drugs, toxic industrial chemicals, pesticides improvised explosive devices, and chemical warfare agents. This presentation will use practical examples to introduce different modes of fluorescence sensing, illustrate the key issues relating to solid-state detection of chemical vapours, and multivariate strategies to achieve selective chemical threat detection.

Solar radiation will be the largest single source of electricity in a low-carbon future. To maximise the potential of solar power, new materials will be needed to harvest and convert solar energy alongside existing photovoltaic technologies. Molecular electronic materials, such as conjugated polymers and molecules, can achieve photovoltaic conversion through a process of photon absorption, charge separation and charge collection. The materials are appealing because of the potential to tune their properties through chemical design and their compatibility with high-throughput manufacture. They are also interesting model systems for photochemical energy conversion because of their parallels with natural photosynthesis. Through a remarkable series of advances in materials design, the efficiency of photovoltaic energy conversion in molecular materials has risen from 1% to around 20% within two decades, surpassing most predictions. We will discuss the factors that control the function of molecular solar cells including the nature of the charge separating heterojunction, and the impact of chemical and physical structure on phase behaviour, energy and charge transport, light harvesting, and loss pathways. Finally, we will address the limits to conversion efficiency in such systems.

We explore the effects of crystal structure and counterion position on the formation of polarons, strongly coupled polarons, and bipolarons using both spectroscopic and X-ray diffraction experiments and time-dependent density functional theory (TD-DFT) calculations. The counterion positions control whether two polarons spin-pair to form a bipolaron or whether they strongly couple without spin-pairing. When two counterions lie close to the same polymer segment, bipolarons can form, with an absorption spectrum that is blueshifted from that of a single polaron. Otherwise, polarons at high concentrations do not spin-pair, but instead J-couple, leading to a redshifted absorption spectrum. The counterion location needed for bipolaron formation is accompanied by a loss of polymer crystallinity, so that bipolarons can form only in disordered regions of conjugated polymer films. Our experiments and calculations also suggest that the ease with which charge carriers can be produced depends on the barrier to transforming the neutral polymer crystal structure into the doped structure that is able to incorporate the counterions.

Semiconducting polymers have broad device application potential, particularly when doped, either chemically or electrochemically, to improve conductivity. Carrier mobility in doped polymers is highly variable, however, and much of that variability stems from strong electrostatic attraction between dopants and their counter-ions. Here, we first explore how polymer and dopant structure can be used to mitigate that electrostatic attraction, considering the interplay between dopant size, polymer chain packing, polymer crystallinity, and doping mechanism. We next consider applications for doped conjugated polymers, focusing on their use as binders in lithium ion batteries. Battery binders are usually chosen only for chemical inertness, but adding electronic conductivity can improve battery cycling. If polymer doping energies are matched to the electrode material, highly conductive binders can be produced. By tuning the side chains, ionic conductivity can further be mixed with electronic conductivity, both of which are needed for fast battery operation.

First, I will discuss interfacial charge generation in ternary blend polymer solar cells based on a conjugated donor polymer, a fullerene derivative acceptor, and a near-IR dye molecule. On the basis of transient absorption analysis, we found rapid charge generation of polymer polarons and fullerene anion upon the photoexcitation of dye molecules, suggesting that dye molecules should be located at the donor/acceptor interface in the ternary blend. Next, I will discuss how energy matching and passivation at the interface between perovskite and hole-transporting layers can suppress interfacial charge recombination effectively. In either case, open-circuit voltage is effectively improved because of suppressed interfacial charge recombination.

A next target in photovoltaic energy conversion can possibly be met by developing perovskite triple or even quadruple junction solar cells. These require developing stable perovskite sub-cells with bandgaps in the range of 1.8 to 2.3 eV, i.e., a range that has not received much attention so far. Guided by photocurrent spectroscopy and absolute photoluminescence spectroscopy, in combination with bulk and interface passivation strategies, tandem and triple junction solar cells with a power-conversion efficiency of 26% have been reached. Photoluminescence of individual sub-cells provides information on the internal voltage in each absorber layer and offers a detailed understanding of the performance-limiting components in the tandem solar cell following prolonged continuous operation.

Solution-processed light-emitting diodes (LEDs) are attractive for applications in low-cost, large-area lighting sources and displays. Organometal halide perovskites can be processed from solutions at low temperatures to form crystalline direct-bandgap semiconductors with intriguing optoelectronic properties, such as high photoluminescence yield, good charge mobility and excellent color purity. In this talk, I will present our effort to boost the efficiency of perovskite LEDs to a high level which is comparable to organic LEDs. More importantly, organic LEDs are difficult to maintain high efficiency at high current densities due to their excitonic nature and low charge mobilities. Low temperature solution-processed perovskite LEDs demonstrate remarkably high efficiency at high current densities, suggesting unique potential to achieve large size planar LEDs with high efficiency at high brightness.

Microcavity exciton-polaritons are bosonic quasiparticles that result from the hybridization of excitons and modes of a confined electromagnetic field in a regime known as strong light-matter coupling. Having a low effective mass, polaritons can undergo condensation, the macroscopic occupation of the lowest energy and momentum state. Two-dimensional (2D) perovskites are promising candidates for polariton condensation due to their high exciton binding energies, low non-radiative recombination rates and strong oscillator strengths. However, despite their optimal optoelectronic properties, there are no reports of room temperature polariton condensation in 2D perovskites and only one unreproduced report at low temperature. In this study, we systematically examine the interplay between the emission from the exciton reservoir and the population of the lower polariton. We gain insights on how the spectral features of the emission of 2D perovskites affect polariton relaxation and onto one of the mechanisms making polariton condensation challenging in 2D perovskites.

Bulk heterojunction organic solar cells (BHJ OSCs) potentially can offer low cost, large area, flexible, light-weight, clean, and quiet alternative energy sources for indoor and outdoor applications. OSCs using non-fullerene acceptors (NFAs) have garnered a lot of attention during the past few years and shown dramatic increases in the power conversion efficiency (PCE). PCEs higher than 19% for single-junction systems have been achieved, but the device lifetime is still too short for practical applications. Thus, understanding the degradation mechanisms in an OSC is crucial to improve its long-term stability. In this talk, I will discuss the degradation mechanisms in BHJ OSCs. We investigated the impact of different blend materials and device structures on the device stability. A combination of characterization methods such as solid state Nuclear Magnetic Resonance (NMR), resonant soft X-ray scattering (RSoXS), AFM, X-ray photoelectron spectroscopy (XPS), Electron paramagnetic resonance (EPR) spectroscopy, and capacitance spectroscopy are employed to gain insight into the device degradation mechanisms. We propose strategies to improve the device stability.

Template-patterned, flexible transparent electrodes (TEs) formed from an ultrathin silver film on top of a commercial optical adhesive – Norland Optical Adhesive 63 (NOA63) – are reported. NOA63 is shown to be an effective base-layer for ultrathin silver films that advantageously prevents coalescence of vapour-deposited silver atoms into large, isolated islands (Volmer-Weber growth), and so aids the formation of ultra-smooth continuous films. 12 nm silver films on top of free-standing NOA63 combine high, haze-free visible-light transparency (T ≈ 60% at 550 nm) with low sheet-resistance (Rs ≈ 16 𝛀/sq.), and exhibit excellent resilience to bending, making them attractive candidates for flexible TEs. Etching the NOA63 base-layer with an oxygen plasma before silver deposition causes the silver to laterally segregate into isolated pillars, resulting in a much higher sheet resistance (Rs > 8 M𝛀/sq.) than silver grown on pristine NOA63 . Hence, by selectively etching NOA63 before metal deposition, insulating regions may be defined within an otherwise conducting silver film, resulting in a differentially conductive film that can serve as a patterned TE for flexible devices.

In 2021 the IOPV-LAB (Indoor Organic Photovoltaic LABoratory) was created bringing together two laboratories from Aix-Marseille University (CINaM and IM2NP) and the company DRACULA TECHNOLOGIES (DT) to lift together the technical barriers to the development of OPV modules processed by ink jet printing dedicated to indoor (IOPV). Here we present our recent results of the IOPV-Lab towards the processing of high efficiency OPV modules with low environmental footprint as well as developing a standard for power conversion efficiency measurements under indoor light. We present the lab to fab transfer from highly efficient NFA based polymer blends using high band gap acceptors to ink jet printed solar cells. Furthermore, the stability of NFA based printed solar cells and modules will be discussed.

Commercialization of flexible perovskite solar cells (or PSCs) is prohibited by environmental instability and low mechanical robustness. We use glancing angle deposition (GLAD) at low substrate temperature to in-situ deposit nanopillar arrays (NaPAs) onto a flexible electrode for an assembly of flexible PSCs. The NaPAs are made of diverse inorganic materials, such as titanium, titanium oxides, tin oxides (functioning as electron transporting layers) and nickel oxides (serving as hole transporting layers). The as-grown NaPAs enhance light transmittance, facilitate light harvesting in perovskites, promote charge carrier transport and collection, facilitate the formation of large perovskite grains, prohibit perovskites from decomposition, and release mechanic stress. All these features cause large-area flexible PSCs to have PCE of >15%, small photovoltaic hysteresis, 10% degradation for approximately 800-hr storage, and 20% degradation by manual bending for around 400 times.

Potential-induced degradation (PID) is a prevalent concern in current commercial photovoltaic technologies that impacts their reliability, with the mechanistic basis for PID being poorly understood. Here we investigate the PID mechanism in perovskite minimodules. Our findings reveal non-uniform degradation in both the photoluminescence intensity and spectral blue shift. Following 60-hour laboratory stress tests, device efficiency drastically decreases by 96%, and the shunt resistance decreases by 97%, accompanied by a significant quantity of Na+ ions (derived from the soda-lime glass) throughout the device structure, leading to a typical PID shunting effect. Interestingly, we observed a rapid recovery of device performance during room-temperature dark storage, in which Na+ ions located close to the glass substrate side rapidly migrate out of the device. Moreover, we also found that the Na+ ions do not appear to diffuse through the grain boundaries but rather their neighboring area and grain interiors, judging by microscopic conductivity mappings.

The power conversion efficiency (PCE) of perovskite solar cells (PVSCs) has been soared to over 26%, which is comparable to the commercial silicon solar cells. However, the problem regarding its long-term stability is still quite a great challenge, which limits their commercial application. Recently, two-dimensional (2D) perovskites, featuring a periodic structure consisting of the 3D components and 2D spacers as a crystalline bulk, have been widely studied due to their low ion migration and extremely high device stability. However, the PCE of 2D PVSCs is low, ascribing to its anisotropy structure and the insulated spacer cations. Besides, its wider bandgap will lead to insufficient light absorption. In this presentation, I will mainly focus on the applications of 2D perovskite materials for highly efficient and stable solar cells. Firstly, the PCE of 2D PVSCs is increased to over 20% by developing series of methods to regulate the perovskite film quality, as well as to reduce the trap state in the perovskite film and at the interface, which favor for charge transport and reducing non-radiative recombination. By interface modification with the 2D space, significant increase in effi

Flexible perovskite solar cells (PSCs) show promise for next-gen photovoltaics, but achieving stability remains challenging, especially between rigid and flexible substrates. This study optimizes flexible PSCs' stability and reproducibility by selecting substrates, refining cleaning processes, and enhancing interfaces. Evaluating various substrates for flexibility, roughness, and perovskite compatibility, a meticulous cleaning protocol removes contaminants, improving perovskite-adhesive interactions. Emphasis on buried interfaces minimizes defects and boosts charge transport. Results show improved PSC efficiency (15.2% to 19.7%) and cycle durability (130 to 850 cycles, bending radius 5mm, reaching T80). Closing the performance gap, these findings advance reliable flexible PSCs for portable electronics, wearables, and building-integrated photovoltaics.

Halide perovskites, promising for next-gen energy tech due to their optoelectronic prowess and cost-effective processing, differ markedly from traditional semiconductors in their dual ionic-covalent bond nature, resulting in a mechanically soft and dynamically disordered lattice. Despite being fragile, their remarkable resilience to stress makes them intriguing. Sensitivity to composition, fabrication, and external stimuli affecting strain necessitates understanding their elusive elastic properties for synthesis and device operation. We performed synchrotron-based X-ray diffraction on lead-halide and double perovskites at low pressures (similar to those experienced during manufacturing), unveiling trends in bulk modulus and thermal expansivity. Greater halide ionic radius led to increased softness, compressibility, and thermal expansivity. Non-cubic systems exhibited axis-dependent compressibility, with A cation exerting a minor effect. Thermal transitions induced lattice softening and negative expansivity in specific axes, underscoring the importance of considering temperature-dependent elastic properties for device stability and performance in halide perovskite.

Lead and tin halide perovskites are currently under intense investigation for their potential applications in optoelectronics, due to their favorable and adjustable semiconducting properties. Despite the potential for widespread adoption in the industrial sector, dry deposition of perovskite films and devices remains a specialized area. Here we will examine the latest developments in the vacuum deposition of perovskite films, focusing on methods to manipulate their morphology and structure. Specifically, we will highlight the impact of factors such as composition, deposition rate, and substrate temperature on properties like luminescence quantum yield and recombination lifetime. We will also present a dry synthetic method to prepare powders and functional disks starting from raw chemical precursors. Lastly, we will show the use of these materials in solar cells and photodetectors.

Solar photovoltaic (PV) energy has been playing an increasingly important role in the world’s energy portfolio. It is becoming a key contributor to the global transition to decarbonized electricity generation. Lead (Pb) halide perovskites have attracted great attention in PV due to their outstanding optoelectronic and defect properties. The research of halide perovskite solar cells continues to boom with device energy conversion efficiency approaching that of single crystal silicon solar cells The discovery of the extraordinary properties enables its application in efficient single-junction and multi-junction solar cells. In this talk, I will present the advance in understanding the optoelectronic properties of halide perovskites. One of the most promising, yet not heavily researched approaches is to make tandem solar cells using materials that function well even when they are polycrystalline and defective. Recent advances with hybrid perovskite semiconductors and their potential use in tandems will be emphasized. The progress of low-voltage deficit in wide bandgap perovskite and its application in high-performance perovskite-silicon tandem solar cells will be discussed.

Mixed-halide wide-bandgap perovskites are key to the development of efficient multijunction solar cells. However, the complex crystallization mechanisms in solution-processed layers introduce heterogeneity in thin films, which limits device performance. This work studies mixed-halide perovskite semiconductors in the 1.8 eV to 2.0 eV optical bandgap range, relevant for tandem and triple-junction photovoltaic devices, and investigates the development of structural and compositional heterogeneity and its impact on device behavior. We find that wide-bandgap layers form wrinkled surfaces, associated with differences in precursor crystallization rates during spin-coating. High-resolution X-ray fluorescence microscopy further allows to correlate the appearance of wrinkles to local chemical heterogeneity, which further lead to local bandgap fluctuations. Finally, sensitive photocurrent spectroscopy measurements allow us to identify an increase in defect density and bandgap disorder as a function of structural and compositional heterogeneity, which accelerates photo-instability through light-induced halide segregation in thin films and solar cells.

Perovskite solar cells report a high level of photoelectric conversion efficiency, while there is a problem that their stability is relatively low. In particular, control is very important because it promotes the deterioration of defective perovskites generated in perovskite crystallization. To this end, although defect passivation through additives has been popularly studied so far, studies on how the amount of function group and the density due to its molecular structure affect perovskite defect passivation and crystallization are insufficient. In this study, the passivation effect due to the presence of the electron donating group and the difference in electron density in a phosphine-based additive was studied. As a result, it was found that the presence and location of the electron donating group had a great influence on the perovskite crystallization, and as a result, excellent power conversion efficiency and high thermal stability were achieved in tris(o-methoxyphenyl)phosphine additive.

The rise of organic semiconductor technology hinges on advancements in organic light-emitting diodes (OLEDs), now integral to displays. Organic photovoltaics (OPV), benefiting from enhanced efficiency and stability, have transitioned from labs to niche markets. This shift coincides with the emergence of small molecule nonfullerene acceptors (NFAs), replacing older electron acceptor materials. Among new opportunities, organic photodetectors (OPDs) stand out, aiming for broad near-infrared (NIR) detection. Tailoring donor:acceptor blends and managing charge carrier recombination are pivotal for efficient and stable NIR light-to-current conversion in OPDs.

Metal Halide Perovskite (MHP) photodetectors exhibit remarkable potential as they combine high specific detectivities, fast response speeds, precise modulation of film optical properties, and seamless integration with read-out integrated circuitry. To attain such performances and maintain them requires an accurate design of charge transport layers. Here we demonstrate how solution processed organic-inorganic interlayers based on metal oxide nanoparticles and polymer mixes enable fast and sensitive visible MHP photodiodes, while warranting stability and pixel-to-pixel reproducibility superior to those of the individual materials. The talk will finish by providing an overview of a broader range of applications of MHP detectors for high and low energy radiation detection.

Organic retinomorphic sensors are particularly effective for motion detection, offering the advantage of in-sensor processing that can remove repetitive static backgrounds. In this study, we investigate the important impact of high-k dielectrics in promoting charge accumulation to increase the intrinsic photo-response of photo-sensitive capacitors within this promising framework. We demonstrate a retinomorphic sensor array to detect the motion of a sample moving at different speeds and directions. These proof-of-concept results represent a promising advance toward scalable integration of organic retinomorphic arrays to meet the growing demand for more efficient motion tracking systems.

Photovoltaics play a vital role in the transition to sustainable and green energy sources. However, conventional rigid and bulky solar cells fail to address the needs of emerging applications where mechanical compliance and high specific power are vital. In this regard, hybrid organic-inorganic halide perovskites attract significant interest owing to their outstanding mechanical and optoelectronic properties. In this contribution, we present transparent-conductive-oxide (TCO)-free and lightweight quasi-2D flexible perovskite solar cells incorporating arylamine organic cations with a champion-specific power of up to 44 W g-1 and an efficiency of 20.1%. Freestanding and unencapsulated flexible devices display admirable environmental stability and mechanical resilience. Rigid devices exhibit excellent operational stability, preserving above 97.2% of their performance after 1000 h of continuous operation at the maximum power point. Moreover, to show the feasibility and potential for upscaling, we demonstrated a photovoltaic module that enables energy-autonomous operation of a hybrid solar-powered quadcopter while constituting only 1/400 of the drone’s weight.

Understanding the chemical factors that dictate long term stability in metal halide perovskite thin films is critical in the optimization of fully commercialized printable energy conversion, display and optoelectronic platforms, X-ray detectors, and photodetectors. The origin of these instabilities has been associated with defects within the perovskite crystal lattice. This talk will discuss established (spectro)electrochemistry-based measurement science approaches to quantify the distribution and energetics of donor and acceptor defects in prototypical perovskite solar cell materials and at buried charge selective interlayers (i.e., hole transport layers). Connections to device performance, benchmarked with time-resolved photoluminescence measurements, will be shown. Results demonstrating the connection between defect quantification and durability will also be discussed in the context of activated corrosion of metal halide perovskites, as probed by dynamic near-ambient pressure X-ray photoelectron spectroscopy.

The use of various chemical treatments, controlling trap passivation and energy level alignment at the perovskite/charge selective contact interface, allowed for impressive strides in the development of highly efficient and stable perovskite solar cells. However, the key challenge for further improvements is the use of a single molecule, able to effectively modify the interfaces, by a simultaneous healing of perovskite defects. In this work, we take up this challenge by adopting a family of organic molecules which bear strongly electron-withdrawing CF3SO2- groups, while some have labile hydrogen and very low pKa (trifluoromethanesulfonimide) and others do not (n-phenyl-bis(trifluoromethanesulfonimide)). Extensive PL, UPS and XPS studies prove that both compounds lead to a simultaneous passivation effect and work function control, leading to enhanced stabilized efficiencies for the as-fabricated planar PSCs. This work paves the way for the use of TFSI-bearing molecules to improve the performance of perovskite optoelectronic devices.

Understanding and minimizing non-radiative recombination pathways from contacts and interfaces is key to enhanced efficiencies in emerging solar cells. Non-radiative recombination in any form, i.e. trap-assisted, or surface recombination of minority carriers at the (wrong) electrode will inevitably lead to lower efficiencies. However, given the fast development of the efficiencies, the stability of both PSCs and OPVs is still not satisfactory. The challenge to suppress non-radiative recombination losses in OPVs and PSCs on their way to the radiative limit lies in proper energy level alignment and suppression of recombination from defects at interfaces, and contacts enabling increased effciencies and lifetimes.

Recently, the power conversion efficiency (PCE) of OSCs is approaching 20%. However, the unsatisfied interface issues limit further improvement in device performance of OSCs. In this presentation, I will introduce our work on interface engineering in OSCs to enhance PCEs and device lifetime, through optimizing physical processes such as exciton separation and/or charge transport/extraction/recombination in the devices and suppressing photodegradation at the interfaces.

There are many problems at the forefront of materials chemistry that are stymied by their inherent complexity. Such problems are characterized by a rich landscape of parameters and processing variables that is combinatorially too large for either an experimental or a computational approach to solve through an exhaustive search. In such cases, the usual approach is an Edisonian trial-and-error approach, which inevitably leaves areas of parameter space largely or wholly unexplored. The problems that we have explored are also characterized by a scarcity of data that are expensive in time and resources to acquire, both experimentally and computationally. This makes it an ideal candidate to solve using a Bayesian optimization approach. For much of a decade, we have used a "chemistry-informed" Bayesian optimization approach to study the solution processing of metal halide perovskites, a promising class of materials for solar cell development. Solution processing offers a low-energy-use and deceptively simple protocol to create electronically active thin films with high solar cell efficiency. We will close with some thoughts on the way the ML field is heading.

Perovskite-based multijunction solar cells are cost-effective strategies to deliver power conversion efficiencies beyond the theoretical limit for single-junction solar cells. In this presentation, we address important factors limiting the performance and longevity of wide-bandgap perovskite solar cells and strategies to achieving record all-perovskite triple-junction solar cells. In addition, by connecting an all-perovskite tandem solar cell with a water electrolysis cell, we demonstrate a solar-to-hydrogen efficiency of 17.8%.

Highly Stable and Efficient Formamidinium-Based 2D Ruddlesden–Popper Perovskite Solar Cells via Lattice Manipulation Fang Zeng, Weiyu Kong, Yuhang Liang, Feng Li, Yuze Lvtao, Zhenhuang Su, Tao Wang, Bingguo Peng, Longfang Ye, Zhenhua Chen, Xingyu Gao, Jun Huang, Rongkun Zheng, Xudong Yang In this study, by finely tuning the FA-based 2D perovskite lattice through spacer cation engineering, a stable lattice structure with balanced distortion, microstrain relaxation, and reduced carrier–lattice interactions is achieved. he optimized FA-based perovskite photovoltaic devices achieve a remarkable power conversion efficiency (PCE) of 20.03%

We present a three-dimensional tomography technique with conductive atomic force microscopy, to obtain internal current mappings of perovskite films subjected to different passivation treatments. Through this 3D current analysis technique, we visualized the three-dimensional structure of currents and defects inside the material resulting from various passivation. Our research provides a novel analytical perspective on the passivation mechanisms within perovskite materials, contributing to a deeper understanding of passivation processes.

The emergence of nonfullerene acceptors (NFAs) has triggered a rapid advance in the performance of organic solar cells (OSCs), endowing OSCs to arise as a promising contender for 3rd generation photovoltaic technologies. Meanwhile, the ultimate goal of OSCs is to deliver cheap, stable, efficient, scalable, and eco-friendly solar-to-power products contributing to global carbon neutrality. However, simultaneously balancing these five critical factors of OSCs toward commercialization is extremely challenging. In this presentation, I will show the self-assembly strategy we developed to reduce the gap of high PCE, long-term stability, green-solvent-processibility, scalability, and low cost of OSCs and demonstrate our green-solvent-processable and open-air-printable OSCs with simultaneously simplified device architecture and enhanced PCE, shelf, thermal as well as light illumination stability. Further, I will present our recent results on the outdoor degradation mechanism study in top-performing systems. Finally, I will summarize our findings on enhancing the commercial viability of OSCs toward commercialized cheap, stable, efficient, scalable, and eco-friendly OSCs.

When an intense laser interacts with a gas of atoms, high-order harmonics are generated. In the time domain, this radiation forms a train of extremely short light pulses, of the order of 100 attoseconds. Attosecond pulses allow the study of the dynamics of electrons in atoms and molecules, using pump-probe techniques. This presentation will highlight some of the key steps of the field of attosecond science.

The increasing global demand for personalized healthcare technologies necessitates a new generation of wearable sensors that are high-performance, low-cost, and compatible with various platforms, including human organs. Low-temperature-processed hybrid and nanostructured materials enable such devices by allowing direct patterning onto 2D and 3D substrates through cost-effective printing processes. Their electronic and mechanical properties can be easily tuned through composition or morphology adjustments. In this presentation, I will describe how this material class facilitates novel wearable medical devices with unprecedented performance. Specifically, I'll focus on creating optical devices for noninvasive physiological measurements, including a high-gain high-speed photovoltage transistor for continuous vital sign tracking and a single-point spectrometer for multi-spectral photoplethysmography. Additionally, I will discuss our recent exploration of using quasi-two-dimensional Dion-Jacobson phase perovskites to achieve photonic structure-integrated light-emitting devices.

Specific emphasis in this talk will be placed on the development of see-through power windows via a new design of semitransparent organic solar cells (ST-OSCs), which allows for the efficient utilization of spectrum-engineered solar photons from the visible to infrared range with both energy generation and saving features.

Organic photodetectors (OPDs) exhibit performance on par with inorganic detectors (e.g. Si) but can be ultrathin, lightweight, flexible and mechanically resilient, opening up opportunities for novel applications including optical sensors for continuous human and plant health monitoring. Here, we develop a high-performance flexible self-powered OPD designed for on-plant optical sensing. The OPD employs an electrode consisting of Ag nanowires (NWs) embedded in a UV-curable resin to achieve a flexible and thin form factor. In addition, the OPD active layer consisting of D18-Cl and Y6 is sequentially cast to reduce dark current. The flexible OPD is demonstrated to effectively detect plant uptake of the rare-earth metal terbium and sense time-dependent chlorophyll fluorescence. Furthermore, we show that the OPDs can be made intrinsically polarization-sensitive by controlling the in-plane alignment of the polymer. The advantages of polarization sensitivity for applications for both human and plant health monitoring are then discussed.

To detect the band-specific optical signals used in many fields, it is necessary to develop spectrally selective photodetection. For such wavelength-selective photodetection or color discrimination, organic photodetectors (OPDs) can offer significant benefits as low temperature and solution processability, chemical versatility, and specific spectral detection range. However to avoid commonly used filters, the design of a narrowing approach that simultaneously achieves a selective detection range with a bandwidth of less than 50 nm and a spectral response of over 20%, remains a challenge. OPDs based on charge collection narrowing (CCN) principle can provide these features. Herein, we realize filter-free band-selective OPDs based on PM6:PC70BM blends as state-of-the-art. Fine adjustment over a bandwidth of 42 nm to be highly selective at 677 nm with a quantum efficiency of 48.4% under an inverse low bias of -2 V is reached. In addition, using a non-invasive and non-destructive encapsulation technique, we demonstrate that these OPD fully retain their high selective peak after 30 days storage in air.

We propose unique anodic nanostructures, consisting of hole-transporting polymers and self-assembled monolayers, to fabricate perovskite solar cells. The so-called, self-adaptive transport layer effectively reduced the loss of open circuit voltage and fill factor. The PCE value could reach 19.63% under 1-sun standard illumination condition. More importantly, the device exhibited high PCEs of 33.54% and 38.16% under illumination of indoor light sources at 200 and 2000 lux, respectively. This indoor PCE at 2000 lux is one of the best values for inverted perovskite devices. Furthermore, a very high efficiency of over 40% was also achieved after an optical enhancing layer was applied. Such indoor PCE at 2000 lux is one of the best values for inverted perovskite photovoltaic devices. Finally, the stability of the devices is also evaluated.

Metal oxide materials are crucial for efficient perovskite solar cells (PSCs) due to their stability and wide bandgap. We introduce a low-temperature intercalation method using p-type nickel oxide (NiO) with cesium carbonate (Cs2CO3) to enable bipolar charge transport in PSCs. The Cs2CO3-intercalated NiO serves as both hole and electron transport layers in inverted and conventional planar PSCs, enhancing electron extraction without compromising hole extraction efficiency. This approach achieves power conversion efficiencies of up to 12.08% and 13.98% for inverted and conventional planar PSCs, respectively, while also providing a potential route for tandem optoelectronics.

The OSC field has been revolutionized through the development of numerous novel non-fullerene acceptors (NFA). The device stability and mechanical durability of these non-fullerene OSCs is critical and developing devices with high performance, long-term morphological stability, and mechanical robustness remains challenging. We will discuss: 1) our current understanding of the phase behavior of OSC donor:acceptor mixtures and the relation of phase behavior and the underlying hetero- and homo-molecule interactions to performance, processing needs (e.g., kinetic quenches), and morphological and mechanical stability; 2) molecular hetero-interactions between the donor and NFA that are not always the geometric mean of the homo-interactions; molecular interactions that are relevant in understanding in rubber-toughening of OSCs with a SEBS additive; and 3) that ~50% of semi-conducting blends investigated so far exhibit re-entrant phase behavior. The results presented and its ongoing evolution are intended to uncover fundamental molecular structure-function relationships that will allow predictive guidance on how desired properties can be targeted by specific chemical design.

Energy transfer between materials in organic photovoltaics often assists energy transport to the site of free charge generation. Here we present a case where the opposite is true: dilute donor molecules sensitizing a fullerene matrix. We show via a combination of time-resolved microwave conductivity (TRMC), femtosecond transient absorption (fsTA), and photoluminescence excitation (PLE) spectroscopy that fast energy transfer from the donor to the acceptor ultimately results in charge transfer, but not photoconductivity. Instead, the excited states are lost as tightly bound charge-transfer states that do not subsequently dissociate to from free charge in this system. This behavior is caused by an asymmetry in the entropy associated with charge transfer in each direction and is well described by a model in which free charge generation is governed by a combination of entropic gain and competition between multiple Marcus-like charge transfer events to a distribution of distances.

The solar power conversion efficiencies of organic solar cells (OSC) have now increased up to 19%, closing the gap with inorganic and hybrid solar cells. The major breakthrough behind the rapid efficiency improvement is the development of non-fullerene acceptor molecules, replacing the traditional fullerene molecules as electron-accepting materials. Understanding the photophysical processes underlying these high-performance materials is crucial to OSC research. In this talk, I will present transient optical spectroscopy and structural analysis results on high-performance OSC blends based on state-of-the-art Y-type small molecule and polymeric acceptors. We find direct evidence that the interfacial D-A percolation plays a key role in suppressing interfacial charge recombination to enable efficient charge generation, and such morphology greatly improves the thermodynamic stability of the blend. Furthermore, we uncovered a new all-optical method for predicting the OSC performance of acceptor molecules, which will be a valuable tool for future material design and screening.

Conjugated hairy-rod polymers, which have emerged as promising photocathode materials for solar-fuel production, are comprised of stiff, low-entropy backbones and complex side-chain substitutions, which collectively affect assembly compared to flexible-chain materials. Here, we unravel the relationship between structural and electronic disorder in a model hairy-rod polymer, PBTTT. We identify a narrow electronic density-of-states (DOS) distribution with weak spatial variations in PBTTT, while the prototypical flexible-chain polymer, P3HT, features an energetically broad, spatially variable DOS. We assign this observation to the fact that PBTTT is structurally homogeneous due to its liquid-crystalline-like behavior, contrary to the structurally heterogeneous, semi-crystalline P3HT. This view is further supported by 2D electronic spectroscopy, which reveals that PBTTT features dynamic electronic disorder, vs. P3HT, which exhibits primarily static electronic disorder. Collectively, our work provides understanding into the disordered energy landscape in conjugated hairy-rod polymers, towards accelerated materials discovery for renewable energy technologies.

Considering the technical standards required for wearable electronics, such as mechanical robustness, the development of fully stretchable OSCs (f-SOSCs) should be accelerated. Concurrently, f-SOSCs offer an intriguing platform for testing the mechanical and electrical properties of new polymeric materials. This presentation will discuss key studies aimed at making each layer of f-SOSCs both stretchable and efficient, with an emphasis on strategies to simultaneously enhance the photovoltaic and mechanical properties of the active layer. I will outline material design strategies to enhance the mechanical robustness of the PSCs as well as their power conversion efficiencies (PCEs). These strategies include; i) incorporating a high-molecular weight polymer acceptor as a tie molecule into active layers, ii) developing new electroactive polymers consisting of hard and soft segments and iii) developing new materials that improve molecular miscibility in the donor-acceptor blends. With these contributions, the f-SOSCs achieving over 14% PCE and high stretchability have been developed.

Immense efforts in the flexible electronics field have led to unprecedented progress and to devices of ever increasing performance. Despite these advances, new opportunities are sought in order to widen the applications of flexible electronics technologies, expand their functionalities/features, with an increasing view on delivering sustainable solutions. We discuss here opportunities the use of multicomponent systems for, e.g., increasing the mechanical flexibility and stability of organic electronic products, or introducing other features such as self-encapsulation and more robust transport. We demonstrate the working principle of semiconductor:insulator blends, examining the different approaches that have recently been reported in literature. We illustrate how organic solar cells (OPV)s can be fabricated with such systems without detrimental effects on the resulting device characteristics even at high contents of the insulator.

First companies report commercial OPV production capacities of >1 million m² per year. These announcements are accompanied by first life cycle analysis (LCA) data of commercial OPV modules, providing more reliable data than previous estimates extrapolating from the lab, allowing to make better estimates on what would it mean to scale OPV to TWp in installed capacity. Using such available commercial data, we analyze the environmental & resource impact as well as cost development of OPV modules when massively scaling OPV. Given their scalable low temperature production processes and little material input, greenhouse gas emissions of OPV modules, currently already only at 25% of the of average silicon PV modules, will drop fast to less than 10%. Similarly, cost are expected to rapidly fall with technological learning, opening up more markets. Finally, we find that there is no foreseeable material bottleneck for OPV modules even when reaching 10s of TWp.

For organic solar cells to be competitive, the light-absorbing molecules should simultaneously satisfy multiple key requirements, including weak-absorption charge transfer state, high dielectric constant, suitable surface energy, proper crystallinity, etc. However, the systematic design rule in molecules to achieve the abovementioned goals is rarely studied. In this work, guided by theoretical calculation, we present a rational design of non-fullerene acceptor o-BTP-eC9, with distinct photoelectric properties compared to benchmark BTP-eC9. o-BTP-eC9 based device has uplifted charge transfer state, therefore significantly reducing the OSC energy loss by 41 meV and showing excellent power conversion efficiency of 18.7%. Moreover, the new guest acceptor o-BTP-eC9 has excellent miscibility, crystallinity, and energy level compatibility with BTP-eC9, which enables an efficiency of 19.9% (19.5% certified) in PM6:BTP-C9:o-BTP-eC9 based ternary system with enhanced operational stability. Ref. Nature Communications (2024) In press

Free charge generation in organic solar cells generally proceeds via (1) the population of CT states after photoexcitation of donor or acceptor, and (2) CT state dissociation into the charge separated (CS) state. To date, most research either studied the combined effect of CT state formation and dissociation on photocurrents without distinguishing individual processes, or focused on improving CT state formation to increase photocurrents, neglecting CT state dissociation efficiency. Investigating dilute donor blends of Fx-ZnPc (x=0-16) and C60 with a range of experimental techniques and DFT, leads us to conclude that CT state dissociation rather than CT state formation presents a major bottleneck for CS generation in fullerene-based blends with low energetic offsets between locally excited (LE) and CT states. With this, our work highlights potential reasons why low offset fullerene systems do not show the same promising performance as those based on non-fullerene acceptors.

The properties of organic functional materials are determined by both their chain structure and the intermolecular interactions. Based on the basic concept of precisely controlling intermolecular interactions, we have developed a series of material systems with specific transport structures by controlling the arrangement and aggregation of organic optoelectronic molecules through the Cl∙∙∙S and Cl∙∙∙π interactions. In particular, we discovered a three-dimensional (3D) network structure in the model molecules with specific chlorine-mediated intermolecular interactions. We also systematically studied the effects of chlorine substitution position, number, and isomerism on the formation of the 3D network structure, which could provide the better molecular design strategy to achieve improved device performance. With the exciton diffusion distance exceeding 40 nm, those materials open a window for the development of quasi-planar heterojunction (Q-PHJ) devices. Compared with bulk heterojunction (BHJ) devices, Q-PHJ devices have a thermodynamically stable donor-acceptor bilayer structure, which can greatly improve device stability for coming practical applications.

The combination of donor (D) and acceptor (A) materials in organic solar cells (OSC) determines the corresponding D:A morphology in solar cells and the so-called golden triangle of OSC, that is, cost, power conversion efficiency (PCE), and stability. However, despite the recent advancement in OSC, determining the optimal material combination for industrialization is still a challenge. Herein, we unveil the optimal material combination that exhibits maximum industrial viability. Specifically, the industrial figure of merit (i-FoM) of 7 OSC categories is calculated and further analyzed, including small molecule donor (SMD):fullerene acceptor, SMD:non-fullerene acceptor (NFA), oligomer donor:NFA, terpolymer:NFA, polymer donor:NFA, polymer donor:polymer acceptor, and single-component materials. Since OSC is approaching wide-scale industrialization, our insights into the successes and challenges of these material combinations, particularly their PCE, photostability, and synthetic complexity (SC) index, offer guidance toward accelerating the industrialization of OSC.

Photon upconversion is a process that combines low-energy photons to form useful high-energy light. There are potential applications in photovoltaics, photocatalysis, biological imaging, etc. Semiconductor quantum dots (QDs) are promising for the absorption of these low-energy photons due to the excellent absorptivity of QDs, especially in the near infrared (NIR). This allows the intriguing use of diffuse light sources such as solar irradiation. In this talk, I describe the development of this organic-QD upconversion platform based on triplet-triplet annihilation, focusing on the dark exciton in QDs with triplet character. Then I introduce the underlying energy transfer steps, starting from QD triplet photosensitization, triplet exciton transport, triplet-triplet annihilation, and ending with the upconverted emission. Design principles to improve the total upconversion efficiency are presented. This talk provides a guide for designing efficient organic-QD upconversion platforms for future applications, including overcoming the Shockley-Queisser limit for more efficient solar energy conversion.

Two-dimensional (2D) perovskites with excellent stability and optoelectronic properties have aroused great interest for use in perovskite solar cells (PSCs). To date, the power conversion efficiencies (PCEs) of state-of-the art 2D-PSCs are non-satisfactory because of higher recombination losses in 2D quantum wells. Here, based on a series of alkylic ammonium spacers (ethylamine to hexylamine) with different chain lengths, we present a strategy via the molecular van der Waals interaction to realize modified crystallization, phase distribution, and quantum-confined behaviors in Ruddlesden-Popper 2D perovskites (n = 4). With the optimal amylamine (AA) spacer, high-quality 2D perovskites featuring well-aligned phase alignments with fewer unfavorable n-value species and a reduced exciton binding energy have been realized, leading to sufficient charge transfers through different n-value components. The devices based on (AA)2MA3Pb4I13 yield a champion PCE of 18.42%, showing an impressive open-circuit voltage of 1.25 V and a fill factor exceeding 0.80.

To fulfill the promise of two-dimensional perovskites (2DPs) for high-performance optoelectronics, we used mechanical exfoliation to obtain n = 1 / n = 3 2DP-heterostructures and ultrafast techniques to characterize charge carriers’ dynamics at interface. In the presence of the heterostructure, we observe the suppression of excitonic-radiative recombination and the introduction of a fast decay channel for excitons (t < 2 ns) which explains more than 80% of the total photoluminescence decay. Such evidence can be explained through ultrafast electron and hole transfer at the heterostructure interface.

The hole transport layer (HTL) plays a very significant role in the performance of perovskite solar cells (PSCs). However, the selection of appropriate HTL is crucial to realizing the stability, cost, and device efficiency of PSCs. In this study, initially, NiCO2O4 structures were synthesized via a hydrothermal route. Further, various characterization techniques were employed to analyze the synthesized materials, including UV-vis spectroscopy (UV), field emission scanning electron microscopy (FESEM), Fourier transform infrared spectroscopy, X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy. The crystal structure, band gap, elemental mapping, surface morphology, site-specific structural, and electronic state of the atom were investigated using XRD, UV, FESEM, TEM, and XPS, respectively. Furthermore, all inorganic lead-free PSC was developed using the spin-coating technique and exhibited improved PCE with spinel NiCO2O4 hole transporting material.