This PDF file contains the front matter associated with SPIE Proceedings Volume 11893, including the Title Page, Copyright information, and Table of Contents.

Perovskite solar cells (PSCs) with an inverted planar architecture have gained enormous attention due to their easy fabrication, simplified device structure, and compatibility with flexible substrates, large-scale production, or tandem cells. The focus of this talk will be on the development of high-performance single-junction inverted PSCs based on a low cost and solution-processable hole transport layer poly[N,N′-bis(4-butylphenyl)-N,N′-bis(phenyl)benzidine] (poly-TPD). The devices have been systematically investigated, consisting of fabrication and optimization, interface modification, and long-term stability. The study aims to increase the open-circuit voltage and power conversion efficiency of the fabricated devices, and disclose their degradation pathway through a range of optical and electrical characterization.

It has been slightly over a decade since metal halide perovskite materials were first used in solar cells. Nowadays it has become one of the most active research fields and continues to progress rapidly on various fronts. My group at OIST is making efforts to use surface science and advanced material characterization techniques to obtain in-depth understanding about perovskite materials and devices. In this talk, I will present our research progress on surface science understanding of perovskite materials and stability.

Interfaces play a key role in determining the performance of perovskite semiconductors. This talk will present a discussion concerning both internal and external interfaces of perovskites. First, I will discuss the characterization and properties of the most critical internal interface - grain boundaries in perovskites. Following this, I will demonstrate “grain-boundary functionalization” as an effective protocol to mitigate the negative impacts and imparting new functions of perovskite grain boundaries. Then, I will present a novel structure of “interpenetrating interface”, which is formed by an interdiffusion reaction between chemically modified perovskite and charge-transporting layers. This structure delivers enhanced physical properties and chemical stability, highlighting the importance of external interface design in perovskite semiconductors. Finally, I will present a perspective on future studies of various perovskite interface, which is stimulated by our recent characterization advances on atomic-scale scanning tranmission electron microscopic (STEM).

Recent advances in organic solar cells (OSCs) based on non-fullerene acceptors (NFAs) come along with reduced non-radiative voltage losses. We show that the non-radiative voltage losses in these state-of-the-art donor:NFA OSCs show no correlation with the energies of charge-transfer electronic states at donor:acceptor interfaces, different from conventional fullerene-based OSCs. Based on a combined temperature-dependent electroluminescence experiments and dynamic vibronic simulations, we have been able to rationalize the low voltage losses in these devices, where we highlight the critical role of the thermal population of local exciton states in decreasing the non-radiative losses. An important finding is that the molecular photoluminescence properties of the pristine materials define the limit of non-radiative voltage losses in OSCs, indicating that it is critical to design high-luminescence-efficiency donor and acceptor materials with complementary optical absorption bands extending into the near-infrared region. We further demonstrate that there is no intrinsic limit for efficient charge separation in OSCs with small non-radiative voltage losses.

In this paper, nanocones array is introduced into bottom silicon cells design. By finite-difference time-domain methods, the absorption efficiency in the range of 300-1100nm has been analyzed, and the structural parameters have been also optimized. Our calculations show that with the increase of the height of the nanocones, the spectra of the top cell and the bottom cell have significant interference effects, and the short wave photons and long wave photons can achieve the maximum light absorption through strict optical management.The absorption enhancement modes of photons at different wavelengths have been analyzed intuitively by the distribution of electric field. These results enable a viable and convenient route toward high efficiency design of perovskite/Si tandem solar cells.

Understanding the fundamental properties of buried interfaces in perovskite photovoltaics is of paramount importance to the enhancement of device efficiency and stability. Studies to date have focused on the top surfaces of the polycrystalline perovskite films, yet non-radiative losses that hinder the power outputs are known to exist at the buried interfaces due to the accumulation of deep-level trap states. However, exploring these issues will become complex when the excess lead halide accumulates at the buried interface featuring non-exposed characteristics. In this work, the buried mysteries in full device stacks will be unveiled by a series of dedicated techniques including the lift-off strategy, the in-situ buried mapping spectroscopy, and the cross-sectional high-resolution microscopy. By establishing the microstructure–property relations, the basic losses at the contact interfaces are systematically presented, which are induced by both the sub-microscale extended imperfections and lead-halide inhomogeneities. Furthermore, an in-depth mechanism for the most popular ammonium-halide post-treatment is explored by exploiting time-related confocal spectroscopic imaging and materials characterizations. The surface ammonium halides could penetrate from the top surface to the bulk, especially the buried interface, and we called the molecule-assisted microstructural reconstruction. Both the bulk and interfacial losses can be considerably mitigated by the use of the passivation-molecule-assisted microstructural reconstruction, which unlocks the full potential for improving device performance. The methodology reported in this work is expected as the starting point to uncover the properties of the buried interfaces of various perovskite compositions and device structures for a broad range of applications including solar cells, light-emitting diodes, photodetectors, and other perovskite optoelectronics.

Display and power are two essential building blocks to support the development of modern electronics. As an industry standard, displays (such as liquid crystal displays or organic light emitting displays) powered by batteries provide a convenient information channel for users. Energy consumption of displays accounts for a large proportion of total energy consumptions of the electronics, such as more than 30% for smartphones. Displays and batteries both have evidenced preceding advancements in the past centuries, independently. For next generation displays, reaching higher resolution and lower power consumption (<10 mW cm-2 for current display technologies) is urgently needed. Naturally, it is also important to realize higher energy density for the development of energy storage technologies. While displays and batteries need to work seamlessly for all the electronics, the development path of these two fields have never converged. Alkali metals are attracting significant attention at the intersect of plasmonics and batteries. On one hand, alkali metal is demonstrated to be a low-loss plasmonic material. Plasmonics, with the unique capability of focusing light into deep subwavelength scale, has long been pursued to achieve high resolution display devices. Tunable plasmonic displays have been successfully achieved by external electrical, chemical or other stimulus. On the other hand, as the lightest metal, lithium (Li) metal is regarded as the holy grail of high energy density anode materials, with the high specific capacity (3860 mAh g-1) and the lowest electrochemical potential (−3.04 V versus the standard hydrogen electrode). we demonstrate a Li metal based dynamic plasmonic color display, which is a precisely-designed nanostructured anode of Li metal batteries simultaneously, with therefore inherited advantages of the dynamic modulation and the extremely low energy consumption. The dynamic display is enabled by the structural plasmonic color pixels based on a Li metal battery. During the continuous and reversible electrochemical transformation, Li metal nucleates and grows on a pre-patterned substrate during the charge process, which leads to the generation and tuning of plasmonic colors. Li metal strips off from the substrate during the discharge process, thus leading to the erasure of the color. The energy storage feature of Li metal batteries can recycle energy and lead to the energy consumption as low as 1.5 mW cm-2 at the dynamic color state and even lower to 0.105 mW cm^-2 at the static color state, vital for energy-efficient display technologies. More importantly, the dual functionalities of the display and power lead to self-powered displays, in which one pixel charges another pixel to release and store energy. Therefore, our results offer a unique opportunity to enable the integrated platform for energy storage and information display down to nanoscale.

Single-layered organic solar cells (OSCs) based on non-fullerene acceptors (NFAs) have been widely concerned attribute to the rapid progress in power conversion efficiency (PCE), which benefits from the continuous optimization of the electronic structure of the materials and the device structures. However, the performance of OSCs is still far behind other photovoltaic devices based on inorganic materials. One fundamental reason is the low charge mobility of organic materials and the complexity of non-equilibrium morphology of optical absorption layer. The next generation of NFA represented by Y6 shows better electronic structure, appropriate frontier energy levels and well matching with various donor materials. The efficiency of Y6-based OSCs has exceeded 18% and maintains a strong upward trend, envisaging a prosperous future for the OSC technology. As a derivative of Y6, the electronic structure of L8-BO was further optimized and the better morphology of the bulk heterojunction (BHJ) blends based on PM6:L8-BO improved the generation and transmission of carriers and reduced the charge recombination, achieving a PCE approaching 19%. The details of optimized multi-length scaled morphology is the key to improving device performance. In this optimized morphology framework, a global match between the photoelectric parameters and the characteristic lengths is realized, leading to effective exciton separation and the efficient carrier transport.

The intrinsic electronic structure of the donor and acceptor materials in the framework of the morphological features determine the output of organic solar cells (OSCs). Constructing the eutectic mixing based on the non-fullerene acceptors (NFAs) could fine-tune the bulk heterojunction (BHJ) thin film morphology as well as their electronic properties. With the formation of large amounts of crystallites, thin film crystallinity is greatly enhanced, accelerating the transportation of the free carriers. The JSC and FF amplification is achieved due to the formation of this kind of eutectic fibrillar lamellae structure, where efficient exciton dissociation occurs with reduced bimolecular and trap-assisted recombination. Suppressed non-radiative energy loss accounts for high VOC, enabling an improved power conversion efficiency (PCE) of 17.86%. These results reveal the basic importance of constructing a well-suited morphology to explore the details of the ultrafast photoelectric process and energy loss mechanism, which is of high demand in next episode OSC fabrication towards commercialization.

How processing solvents influence the overall photovoltaic performances of polymer solar cells (PSCs) remains unclear in various recently emerged new material systems. Here we systematically studied this issue by integrating an extensively used poly (3-hexylthiophene) (P3HT), or a recently developed conjugated polymer P2F-EHp, with different non-fullerene acceptors. The P3HT based devices processed with the non-halogenated solvent, 2-methylanisole in presence of 1-methylnaphthalene as solvent additive, exhibit reduced bimolecular and trap-assisted monomolecular recombination, facile charge extraction and enhanced charge carrier mobilities. Morphological investigation reveals that the optimizing crystallites, phase purity as well as nanofibrous structure is effective to the enhancement of charge generation and transport. Note that P3HT:O-IDTBR based devices processed with these non-halogenated solvents exhibit an impressive power conversion efficiency of 7.1% with a high fill factor of 75.09% on a device area of 0.05 cm2, and the efficiency remained 6.89% even in a device with large active layer area of 1 cm2 with promising thermal stability. It is also noted that efficient PSCs consisting of P2F-EHp and non-fullerene acceptors of IT-4F and IT-4Cl were developed via optimizing non-halogenated toluene:o-xylene co-solvent. The detailed investigation of film morphology demonstrated that the co-solvent appeared to assist the manipulation of crystal coherent lengths and effectively decrease the phase separation of the corresponding blend films. Of particular importance is that this material system is compatible with the low-cost blade-coating technique and can be processed under ambient conditions without post-treatment. A remarkable power conversion efficiency of 10.1% was achieved by blade-coating the P2F-EHp:IT-4F:IT-4Cl blends in air. The results indicated that using non-halogenated solvents is a promising candidate for constructing efficient PSCs toward practical applications.

In many fields of physics, there is a common inverse source problem, that is, there is a measured optical or electrical signal intensity distribution or scattering differential cross section to retrieve the lost phase information, so as to reconstruct the full wave function. The phase recovery of imaging system is one of these typical problems. The model and experiment based on theory play a role in the development of system optics. And then, we have obtained effective solutions.

Photoanodes based on titanium dioxide (TiO₂) are ubiquitous in various molecular devices for solar energy conversion and storage.[1] Lanthanide doping of TiO₂ (LTO) is among the most explored materials with tremendous potential towards efficient charge transport mesoporous layer as well as improving the photocatalytic activity in both solar cell and solar fuel devices.[2, 3] In this work, presented a comprehensive investigation of improved performance of Samarium (Sm³⁺)-doped TiO₂ based dye-sensitized solar cells (DSSC) and Photo-electrochemical (PEC) devices and established the optimum Sm³⁺ doping of TiO₂ by characterizing the different Sm³⁺concentrations (0.1-0.5 mol%). Various techniques, namely, X-ray diffraction (XRD), scanning electron microscope (SEM), UV-VIS absorption spectroscopy, are employed for an all-inclusive characterization of the prepared Sm-TiO2 samples. The dielectric measurements on Sm-TiO² pellets established the best electrical conductivity exhibited by Sm (0.4%)-TiO². Synthesis protocols are followed based on earlier work.[3] The photoanodes based on prepared Sm-TiO₂ are deposited on FTO substrates and are used to fabricate DSSC and PEC devices. Commercial N719 dye-based DSSC devices are fabricated and tested. Devices with Sm(0.3%)-TiO₂ exhibited power conversion efficiency (η) ≈ 6.4%, which is almost 100% improvement on devices with undoped-TiO² that exhibited η: 3.4% as shown in Figure 1. Time-resolved PL-quenching measurements evidenced better electron-injection at dye/Sm (0.3%)-TiO₂ interface. Similarly, PEC devices presented higher current density at 1.2 V vs RHE potential for Sm (0.3%)- TiO₂. This enhancement corroborates the EIS measurements presenting lower charge transfer resistance values for devices with Sm (0.3%)-TiO₂.