This PDF file contains the front matter associated with SPIE Proceedings Volume 10736, including the Title Page, Copyright information, Table of Contents, Author listing, and Conference Committee listing.

Since the 1st OLED TV product came out in the market, OLED has gone through continuous technology development and remarkable achievement. As the one and only OLED TV panel-maker, LG Display is providing a whole new value and differentiated viewing experience with the most innovative OLED products. As the future display trend, OLED is truly changing our lifestyle and creating another future.

Electrical doping of organic semiconductors increases conductivity and reduces injection barriers from electrode materials, both of which effects can improve the performance of organic light-emitting diodes (OLEDs). However, the low electron affinities of typical OLED electron-transport materials make the identification of suitable n-dopants particularly challenging; electropositive metals such as the alkali metals are not easily handled and form monoatomic ions that are rather mobile in host materials, whereas molecular dopants that operate as simple one-electron reductants must have low ionization energies, which leads to severe air sensitivity. This presentation will discuss approaches to circumventing this issue by coupling electron transfer to other chemical reactivity. In particular, dimers formed by certain highly reducing organometallic sandwich compounds and organic radicals can be handled in air, yet have effective reducing potentials, corresponding to formation of the corresponding monomeric cations and contribution of two electrons to the semiconductor, of ca. –2.0 V vs. ferrocene. These values fall a little short of what is required for typical OLED materials; approaches to further extending the doping reach of these dimers will be described. One such approach involving photoirradiation of a dimer:semiconductor blend leads to metastable doping of a material with a redox potential of –2.24 V, which allows the fabrication of efficient OLEDs in which even high-workfunction electrodes, such as indium tin oxide, can be used as electron-injection contacts.

A new and facile procedure for the preparation of 6,6′-diiodo-5,5′-dibromo-3,3′-dimethoxylbiphenyl has been found. From this compound, a general synthetic strategy for the preparation of 1,8-dibromo-9-heterofluorenes will be developed. The Synthesis of 1,8-dibromo-9-heterofluorenes will open the door to new classes of inorganic and organometallic conjugated polymeric materials of polyheterofluorenes.

Current materials leaders in OLED technology are largely based on phosphorescent iridium complexes and Thermally Activated Delayed Fluorescence (TADF) materials which emit by harvesting light from all excited states ensuring nearly 100% internal quantum efficiency (IQE). Although, high efficiency red, green and blue OLEDs were realized, very short operating stability remains a fundamental challenge for blue OLEDs. Here we present our materials design strategy. We have recently designed numerous linear coinage metal complexes with efficient photo- and electroluminescent properties.[1,2] Our materials are composed of the donor and acceptor ligands which are linked by a coinage metal atom. Linear geometry of coinage metal complexes enables rotational flexibility. Rotation about the metal-ligand bond allowed us to tune the energy gap between singlet and triplet excited states. When the gap is close to zero, facile intersystem crossing and reversed intersystem crossing are possible which enables efficient singlet and triplet excited state harvesting. Depending on the value of the energy gap we have designed various functional materials with phosphorescent or delayed fluorescence properties. As a proof of concept, we fabricated OLED devices with exceptionally high external quantum efficiencies (>28% EQE) in both solution-processed and vacuum-deposited OLEDs.[3] Power and current efficiency are comparable to or exceeding state-of-the-art phosphorescent OLEDs and quantum dot LEDs. Our materials possess short excited state lifetime (100-300 ns) for the delayed emission which is highly important for the fabrication of the long-lived OLEDs. [1] A.S. Romanov, D. Di, L. Yang, J. Fernandez-Cestau, C.R. Becker, C.E. James, B. Zhu, M. Linnolahti, D. Credgington, M. Bochmann, Chem. Commun., 52, 6379 (2016) [2] A.S. Romanov, C.R. Becker, C.E. James, D. Di, D. Credgington, M. Linnolahti, M. Bochmann, Chem. Eur. J., 23, 4625 (2017). [3] D. Di, A.S. Romanov, L. Yang, J.M. Richter, J.P.H. Rivett, S. Jones, T.H. Thomas, M.A. Jalebi, R.H. Friend, M. Linnolahti, M. Bochmann, D. Credgington, Science, 356, 159 (2017)

Organic materials that display thermally activated delayed fluorescence (TADF) are a striking class of functional materials that have witnessed a booming progress in recent years. The small ΔEST in TADF-based systems prompts highly efficient RISC from T1 to S1 states, and consequently both singlet and triplet excitons can be harvested for light emission. For the last five years, a tremendous amount of TADF molecules have been reported based on the manipulation of the intramolecular charge transfer as well as the HOMO-LUMO overlap. Beyond this strategy, there is an emerging approach that simply involves intermolecular charge transfer between physically blended electron donor and acceptor molecules for high efficiency TADF-based OLEDs (via exciplex formation). This is because the exciplex-based systems can realize relatively small ΔEST (0–0.05 eV) much more easily since the electron and hole are positioned on two different molecules, thereby giving small exchange energy. Consequently, exciplex-based OLEDs have the possibility to maximize the TADF contribution and achieve theoretical 100% internal quantum efficiency and solve the challenging issue of achieving small ΔEST in organic systems. However, research on exciplex-forming materials is still at a growing stage, and consequently, new molecules with remarkable electro and or photo-physical property are still being explored. Thus, by focusing on the development of exciplex systems, we shall have the prospective of achieving the demands for high-efficiency and high stability OLED devices. In this conference, we will report our updated results of new efficient exciplex systems, and exciplex-hosted fluorescent and phosphorescent OLEDs with high efficiency and high stability.

Current OLED displays rely on a circularly polarised (CP) filter to enhance contrast by trapping ambient light inside the display. However, this means that 50% of the randomly polarised light emitted from each OLED pixel never leaves the screen, halving display efficiency and operational lifetime. One simple route to fabricate CP-emitting OLEDs is to use electroluminescent (EL) polymer – small molecule blends. Our approach is to pair a chiral small molecule with a non-chiral device optimised polymer, which allows for CP-dependent applications while retaining much of the performance properties of the original polymer. Previously circularly polarised polymer emission has been achieved via thick cholesteric stacks of liquid crystalline polymers, where linearly polarised light becomes circularly polarised. Here we show that it is possible to control whether cholesteric packing or chiral dipole dominates emission using film thickness; remarkably this allows us to change the handedness of the CP EL emission in the same materials system. We compare how the chemical structure of the non-chiral polymer and post-deposition processing impacts the chiroptical response of the resulting device, in an effort to provide a set of design rules for future high performance CP-OLEDs. We demonstrate a liquid-crystalline light emitting polymer with a record high induced absorption dissymmetry factor, which additionally shows no change in device characteristics (no trapping, etc) in the blends, as well as strong CP-PL and EL emission.

We review the progress in modeling of charge transport in disordered organic semiconductors on various length-scales, from atomistic to macroscopic. This includes evaluation of charge transfer rates from first principles, parametrization of coarse-grained lattice and off-lattice models, and solving the master and drift-diffusion equations. Special attention is paid to linking the length-scales and improving the efficiency of the methods. All techniques are illustrated on an amorphous organic semiconductor, DPBIC, a hole conductor and electron blocker used in state of the art organic light emitting diodes. The outlined multiscale scheme can be used to predict OLED properties without fitting parameters, starting from chemical structures of compounds.

Excited charge transfer complexes (Exciplex) formed between donor and acceptor materials are frequently encountered in organic photonic devices such as in organic light emitting diodes and organic photovoltaics. Formation of exciplexes can be easily identified by the observation of the red shifted emission from those of the component molecules. Generally the PL efficiency of the exciplexes is low so that OLEDs are designed not to form exciplexes at the organic/organic junctions. Formation of exciplexes at the D/A junction is also to be avoided in OPVs since it reduces the dissociation probability of geminate electron-hole pairs formed at the interface. In this presentation we will firstly discuss on the nature of exciplex including the electronic structure, emission processes and diffusion. Further discussion will be given to the application of exciplex forming systems as the triplet harvesting fluorescent molecular system and as the co-host for phosphorescent and fluorescent dopants for ultimate efficiency in OLEDs.

The fundamental scientific challenge for organic light emitting diodes (OLEDs) is to successfully manage electronic spin. The excited state can only give out light if it can decay to the spin-0 ground state. Finding ways of harvesting light from spin-1 excitations has shaped OLED technology for the last three decades, since the choice of strategy to achieve this necessarily impacts materials design, device architecture, and the processes limiting device lifetime. Here we demonstrate a new approach to rapid triplet harvesting. We introduce a novel class of linear donor-bridge-acceptor light-emitting molecules which twist in their excited states, changing the coupling between electron and hole.(1) These enable doped polymer LEDs with near-100% internal quantum efficiency even at high brightness.(2) Our solution-processed OLEDs achieve current efficiency, power efficiency and brightness comparable to or exceeding those of state-of-the-art vacuum-deposited OLEDs and quantum dot LEDs. Using time-resolved spectroscopy, we establish that luminescence via triplets occurs on 100s of ns timescales at ambient temperature, after reverse intersystem crossing to singlets. We find this occurs because molecular geometries exist at which the singlet-triplet energy gap (exchange energy) is close to zero, such that rapid interconversion is possible. Unlike other low exchange energy systems, substantial oscillator strength is sustained at this point. We describe recent experimental and theoretical evidence for emission from these materials and show how it depends strongly in the interplay between rotational energetics, temperature, oscillator strength and the nanomorphology of the emissive layer. This gives us new tools to control emission colour and rate. Doing so, we tune emission from green to sky-blue, and achieve EQE at 1000 cdm-2 of nearly 30%. Based on this molecular motif, we realise new designs for molecular emitters realising sub-microsecond triplet emission and low roll-off in devices across the visible spectral range. 1. A. S. Romanov et al., Copper and Gold Cyclic (Alkyl)(amino)carbene Complexes with Sub-Microsecond Photoemissions: Structure and Substituent Effects on Redox and Luminescent Properties. Chem. - A Eur. J. 23, 4625–4637 (2017). 2. D. Di et al., High-performance light-emitting diodes based on carbene-metal-amides. Science. 356, 159–163 (2017).

Organic Light Emitting Diodes, OLEDs, are now a common feature in mobile phones and ultrathin televisions. Light generation by electroluminescence in the best OLEDs can have 100% internal charge to photon conversion efficiency. This requires very efficient triplet to singlet excited state harvesting, and has been the strict preserve of electrophosphorescence heavy metal complex emitters until now. However, recently it has been discovered that all organic, donor-acceptor (DA) charge transfer molecules can also yield such efficient triplet harvesting and OLEDS with 100% internal efficiency can be fabricated. Here the process of triplet harvesting is by thermally activated delayed fluorescence, ‘TADF’, i.e. E-type delayed fluorescence, and in this talk I shall elucidate how this triplet harvesting mechanism works, including the mechanism that allows very efficient reverse intersystem crossing in a non heavy metal containing molecule, second order vibronic coupling spin orbit coupling. 1, 2 Detailed photophysical measurements of intramolecular charge transfer (ICT) states in the solid state will be used to guide our interpretation. Temperature dependent time resolved emission, delayed emission and photoinduced absorption are used to map the energy levels involved in molecule decay, and through detailed quantum chemical modelling, electron exchange energies and other energy barriers of the systems are determined with the various excited states involved in the reversed intersystem crossing mechanism elucidated. From these measurements rates of rISC can be obtained. This will be explained. One concern over TADF has been the potential trade off between rISC rate and PLAY because of the orthogonality of the mechanisms controlling these two key photophysical processes. From a new design of TADF molecule, we will demonstrate that it is indeed possible to achieve both high PLQY (100%) and a rISC rate > 107 s-1, seemingly impossible from the original description of rISC and TADF. This gives a new design criterion for TADF emitters. Our vibronic coupling second order spin orbit mechanism has been used to explain the observed photophysical phenomena and from further quantum chemical helps to explain how this paradox can be overcome. With very fast risk and high PLQY comes low efficiency roll-off at high brightness. References 1. Etherington, M. K., Gibson, J., Higginbotham, H. F., Penfold, T. J. & Monkman, A. P. Revealing the spin-vibronic coupling mechanism of thermally activated delayed fluorescence. Nat Commun 7, 13680 (2016). 2. Gibson, J., Monkman, A. P. & Penfold, T. J. The Importance of Vibronic Coupling for Efficient Reverse Intersystem Crossing in Thermally Activated Delayed Fluorescence Molecules. ChemPhysChem 1–7 (2016). doi:10.1002/cphc.201600662 3. Dias, F. B. et al. The Role of Local Triplet Excited States in Thermally-Activated Delayed Fluorescence: Photophysics and Devices. Adv. Sci. 3, 1600080 (2016). 4. M.K. Etherington, F. Franchello, J. Gibson, T. Northey, J. Santos, J.S. Ward, H.F. Higginbotham, P. Data, A. Kurowska, P.L. Dos Santos, D.R. Graves, A.S. Batsanov, F.B. Dias, M.R. Bryce, T.J. Penfold, A.P. Monkman, Regio- and conformational isomerization critical to design of efficient thermally-activated delayed fluorescence emitters, Nature Communications 8, 14987 (2017).

Our research group is currently conducting basic research on organic light-emitting diodes (OLEDs). Recently, we have successfully developed a series of blue and green TADF emitters for OLEDs realizing high external quantum efficiencies through high-throughput screening based on quantum chemical calculations. However, even using highly efficient emitting materials, the device performance depends on the device structure and aggregated state of organic molecules in the device. To understand the origin of the device performance, both theoretical and experimental approaches are important. In this regards, we have also carried out multiscale simulations and solid-state NMR (ssNMR) analysis of organic amorphous thin films. The ssNMR is the powerful technique for the detailed experimental analysis of amorphous aggregated materials, which has been difficult by typical diffraction methods because organic molecules in OLEDs are in the amorphous state. However, the low sensitivity of ssNMR compared to other analytical methods has always been a crucial problem. Recently, dynamic nuclear polarization enhanced ssNMR (DNP-ssNMR) has become popular for the sensitivity enhancement technique for ssNMR. In this presentation, we show the analysis of molecular orientation of an organic semiconducting material in an amorphous thin film state using DNP-ssNMR.

Exciplexes formed by intermolecular charge transfer between electron-donating and electron-accepting molecules have attracted much attention because of their triplet harvesting characteristics for highly efficient OLEDs. Similar to thermally activated delayed fluorescence (TADF), exciplex exhibit an extremely small singlet-triplet energy splitting, and allow upconversion from triplet states to singlet states. Here, we will show our recent results on high performance OLEDs based on exciplex hosts and emitters. Phosphorescent white OLEDs with simple structure were successfully fabricated by doping a blue emitter in the exciplex host and then inserting an ultrathin nondoped orange layer within the blue emissive zone. By optimizing the location of the orange emitter, a high power efficiency of 75.3 lm/W was achieved in the phosphorescent white OLED with reduced efficiency roll-off. Hybrid white OLEDs were fabricated by using exciplex as both of the blue fluorescent emitter and the host for phosphorescent emitters. An exciplex-sandwich emissive architecture was designed to precisely manipulate the exciton allocation. And a high external quantum efficiency of 28.3% and a high power efficiency of 102.9 lm/W were realized in the hybrid white OLEDs, which remain as high as 25.8% and 63.5 lm/W at 1000 cd/m2. Most recently, we proposed a method by exciplex engineering to fabricate fluorescent OLEDs with high efficiency and low efficiency roll-off, which could open a useful avenue to design all-fluorescent white OLEDs without TADF emitters for high performance lighting.

Organic solid-state lasers (OSSLs) have been widely investigated during the past decades, owing to their amenability to low-cost and low-temperature processing, compatibility with plastic substrates, and broad spectral tunability. A variety of optical resonators have been applied for optically pumped OSSLs, including planar waveguide Fabry-Pérot (FP) microcavity, distributed feedback (DFB), whispering-gallery mode (WGM) microring microresonator, and photonic band-gap structures. Nevertheless, electrically driven OSSLs remain still a great challenge, partially because the conflicting requirement between large stimulated emission and high charge carrier mobility narrows the range of organic semiconductor gain materials available for electrically driven OSSLs. Recently, we demonstrated that organic microcrystal with well-defined dimensions and different polymorphisms can serve as microresonators for fundamental investigation of optical confinement effect on laser behaviors, such as nanowire FP and microdisk WGM microlasers. Moreover, organic single crystals are ideal for use as high-mobility materials, because their long-range ordered structures minimize traps and are free from grain boundaries. Therefore, organic microcrystals provide a platform to combine high carrier transport, efficient optical gain, and microresonator together on the way to develop electrically pumped organic lasers. In this talk, I will present our research on the photonic performance of molecular microcrystal microcavities and the latest breakthroughs toward organic microlaser devices. Overall, organic microcrystals bring tunable optical properties based on molecular design, size-dependent light confinement in low-dimensional structures, and various device geometries for nanophotonic integration.

Although flexible optoelectronic devices can be easily fabricated by integrating OLEDs on flexible substrates, this technique suffers from the rapid growth of the non-emitting area due to the oxygen and moisture degradation of reactive electron injection layer materials such as alkali metals. Flexible substrates that can completely block oxygen and moisture are essential for extending the lifetime of flexible devices, but such flexible substrates cannot be easily fabricated. In recent years, inverted OLEDs (iOLEDs) with a bottom cathode have been intensively studied as an ideal structure for realizing air-stable OLEDs. As an alternative to the alkali metals that are commonly used in conventional OLEDs, metal oxides and organic interlayers such as polyethylene imine are employed in most reported iOLEDs. Despite the recent advances in the iOLED technology, the development of interlayers that can prevent the decrease in brightness caused by iOLED operation is lacking. Here, we report the design strategy of an interlayer for the fabrication of efficient and stable iOLEDs. The efficiency and the operational lifetime of the optimized iOLED were comparable to that of the conventional OLED that used the same emitter. Two flexible displays were fabricated to ascertain the feasibility of the application of the interlayer to real devices and the air stability of the iOLED-based devices: one using iOLEDs and the other using conventional OLEDs. The iOLED-based flexible display emits light over 1 year under the simplified encapsulation though the conventional OLED-based flexible display shows almost no luminosity only after 21 days under the same encapsulation.

Organic light-emitting diodes (OLEDs) are an excellent technology for small and large display applications alike and further raise hope to complement solid state lighting in the future. All of these scenarios require OLEDs to operate at their best performance with respect to both wall-plug efficiency and device stability. Given the softness of the organic materials and their virtually unlimited molecular catalogue, this optimization progresses but slowly. In this presentation, we discuss the potential of organic materials processed as so-called ultrastable glasses to improve both efficiency and device lifetime. Ultrastable glasses are formed when the layers are grown by physical vapor deposition on substrates which are held slightly below the glass transition temperature of the respective material. In this study, we selected TPBi as a host material with comparably high Tg of 122 °C [2,2',2"-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole)] for four different phosphorescent emitters, i.e. one blue, two green, and one red Ir-complexes). Compared to devices prepared at room temperature, we see significant enhancements of the external quantum efficiency and device lifetime and further, a clear correlation with the growth properties of the glass forming materials, i.e. the host:guest system.

We will present a light emitting touch-responsive device (LETD) for instantaneous visualization of pressure mapping. The LETD integrates an organomental halide perovskite polymer composite emissive layer and a flexible silver nanowire composite transparent electrode. The composite emissive layer contains methylammonium lead bromide (MAPbBr3) nanocrystals uniformly dispersed in a polyethylene oxide matrix and emits an intense green luminescence. The polyethylene oxide matrix promotes the formation of small perovskite grains and a pinhole free composite film. The composite transparent electrode is separated from the emissive layer with a spacer. When a local pressure is applied, a Schottky contact is formed instantaneously between the metal and the emissive layer, and electroluminescence is produced at low voltages. The LETD is transparent, and can be bent when polyethylene terephthalate is used as the substrate. The device has fast response and can be pixelated to offer potentially new applications in robotics, motion detection, finger print devices, and interactive wallpapers.

Light emission in organic semiconductors is governed by the spin of excitons formed upon electrical excitation. Conventionally, 25% of excitons form as emissive singlets and 75% form non-emissive triplets. Exceeding this limit for OLEDs requires designing new materials. Developments in molecular design have allowed utilization of triplet excitons through either direct phosphorescence (1) or secondary processes converting a triplet into a singlet via a spin flip, creating “delayed” fluorescence. (2) Thermally Activated Delayed Fluorescence (TADF) has provided guidelines for creating donor-acceptor molecules, but the effects governing spin dynamics are still being explored. Increasingly, there is consensus that intersystem crossing,(ISC) cannot be understood from a static picture of the molecules; a more dynamic approach is necessary. Carbene Metal Amide (CMA) emitters (3) provide an excellent example, displaying large spectral shifts due to conformational reorganisation and highly variable intersystem crossing rates. In solid films, they have produced solution processed green OLEDs with record efficiencies. Here we show, starting from the green CMA archetypes, we can alter the molecular design to probe the effects of steric hindrance, spin-orbit coupling, and dipole strength on the emission properties. Using fast time resolved cryogenic PL spectroscopy we demonstrate the impact of changing the metal bridge atom on ISC, and explore high molecular weight variants for flexible electronics. We demonstrate these emitters can be tuned across the visible spectrum whilst retaining similar photophysical properties, and achieve efficient OLED devices via both solution and vacuum processing. We discuss their structure property relationships for emission, explore a new set of high efficiency OLED dopants, and provide fundamental insight into their spin conversion mechanism. From these studies we derive the first set of design rules for this new class of organometallic TADF emitters. 1) Very high-efficiency green organic light-emitting devices based on electrophosphorescence, Baldo et al. Appl. Phys. Lett. 1999 2) Highly efficient organic light-emitting diodes from delayed fluorescence. Uoyama et al. Nature 2012 3) High-performance light-emitting diodes based on carbene-metal-amides, Di et al. Science, 2017

Transparent organic light-emitting diodes (OLEDs) have shown the amazing applications in full-color flat panel displays and solid-state lighting due to their prominent advantages, including low power consumption, light weight, wide color gamut, fast response time and high contrast. To realize high-performance transparent OLEDs, a major research direction is to develop the alternative transparent electrodes with superior optical and electrical properties for replacing the opaque metal top electrodes that are commonly used in bottom-emission OLEDs. Various materials and structures have been proposed to function as transparent conductive electrodes. Metal-dielectric composite electrode (MDCE) has been regarded as an effective TCE for flexible devices in terms of mechanical flexibility, electrical conductivity, optical transparency, and large-area film uniformity. Whilst MDCE may be an ideal candidate to replace ITO, several technical challenges should be overcome when using MDCEs as transparent electrodes in transparent OLEDs. First, the presence of thin metal films in MDCEs will cause surface plasmonic (SP) loss at the metal-dielectric interface due to the oscillation coupling between free electrons at the metal surface and the emitting dipoles. Second, an optical microcavity effect is inevitable with the use of a planar MDCE structure, leading to the spectral and angular dependence of the emission characteristics. Herein, an effective nanostructured metal/dielectric composite electrode (NMDCE) on plastic substrate is applied to transparent OLEDs with an ultrathin metal alloy film for optimum optical transparency, electrical conduction and mechanical flexibility. By combining an light-extraction structure for broadband and angle-independent outcoupling of white emission, the waveguided light and surface plasmonic loss can be remarkably reduced in white flexible OLEDs, resulting in a substantial increase in the external quantum efficiency and power efficiency to ~70% and 160 lm/W.

Dimethyl sulfoxide (DMSO) and ethylene glycol (EG) solvent treatment of conducting polymer poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) were studied using multiscale analysis and dissipative particle dynamic (DPD) simulations. The DPD inter particle repulsion parameters and intramolecular bonding parameters were obtained by reverse mapping of a series of molecular dynamic simulations similar to that used in the earlier contributions. The solvent treatments were found to cause three effects on PEDOT polymer chains at molecular level, increasing rigidity in monomer-monomer bending, decreasing rigidity in monomer-monomer stretching, and decreasing repulsion among monomers. Consequently, these effects lead to PEDOT micro phase segregation and semi-ordered local region formation within and/or between polymer chains. Since the reduction of repulsion among PEDOT monomers can only be caused from selective π−π staking, the formation of these semi-ordered (crystal like) local region may allow charges to bypass local disordered region within the polymer chain and hopping between individual polymer chains, thus, enhance electrical conductivity in orders of magnitude. The implication on PSS:PEDOT:PFI are discussed.

While the field of perovskite-based optoelectronics has mostly been dominated by photovoltaics, light-emitting diodes and transistors, semiconducting properties peculiar to perovskites make them interesting candidates for innovative and disruptive applications in light signal detection. Perovskites combine effective light absorption in the broadband range with good photo-generation yield and high charge carrier mobility, which combination provides promising potential for exploiting sensitive and fast photodetectors that are targeted for image sensing, optical communication, environmental monitoring, or chemical/biological detection. Currently, organic-inorganic hybrid and all-inorganic halide perovskites with controlled morphologies of polycrystalline thin films, nano-particles/wires/sheets, and bulk single crystals have shown key figure-of-merit features in terms of their responsivity, detectivity, noise equivalent power, linear dynamic range, and response speed. The sensing region has been covered from ultraviolet–visible–near infrared (UV–Vis–NIR) to gamma photons, based on two- or three-terminal device architectures. Diverse photoactive materials and devices with superior optoelectronic performances have stimulated attention from researchers in multidisciplinary areas. We offer a comprehensive overview of the recent progress of perovskite-based photodetectors, focusing on versatile compositions, structures, and morphologies of constituent materials, and diverse device architectures toward the superior performance metrics. Combining the advantages of both organic semiconductors (facile solution processability) and inorganic semiconductors (high charge carrier mobility), perovskites are expected to replace commercial silicon for future photodetection applications. The optical and electronic properties of noble metallic nanoparticles can be exploited to enhance the performance of inorganic/organic photodetectors. We integrated a uniformly-distributed layer of Au nanorods (AuNRs) into vertically-structured perovskite photoconductive photodetectors and report, as a result, perovskite-AuNR hybrid photodetectors that exhibit significant photocurrent enhancements. Ultimately it achieves a responsivity of ~320 A/W at a low driving voltage of -1 V. This is an improvement of 60% compared to the responsivity of pristine devices (~200 A/W). The high responsivity and low driving voltage place this device among the highest-performing perovskite-based thin-film photoconductive photodetectors reported. We characterized the stability and linearity of the photoresponse following repeated light/dark cycles. The hybrid device also shows a fast response (with the decay time of ~95 ns) compared to pristine devices (~230 ns). The improvements in photodetection performance are attributed to plasmon-enhanced optical absorption, as well as advances in charge extraction and transport. Metal halide perovskites have rapidly advanced thin film photovoltaic performance; as a result, the materials’ ob-served instabilities urgently require a solution. Using density functional theory (DFT), we show that a low energy of formation, exacerbated in the presence of humidity, explains the propensity of perovskites to decompose back into their precursors. We find, also using DFT, that intercalation of phenylethylammonium between perovskite layers in-troduces quantitatively appreciable van der Waals interactions; and these drive an increased formation energy and should therefore improve material stability. Here we report the reduced-dimensionality (quasi-2D) perovskite films that exhibit improved stability while retaining the high performance of conventional three-dimensional perovskites. Continuous tuning of the dimensionality, as assessed using photophysical studies, is achieved by the choice of stoi-chiometry in materials synthesis. We achieve the first certified hysteresis-free solar power conversion in a planar per-ovskite solar cell, obtaining a 15.3% certified PCE, and observe greatly improved performance longevity. The same protocol was applied to develop highly stable and efficient photodectors in diverse device configurations. Organometal halide perovskites exhibit large bulk crystal domain sizes, rare traps, excellent mobilities, and carriers that are free at room temperature – properties that support their excellent performance in charge-separating devices. In devices that rely on the forward injection of electrons and holes, such as light-emitting diodes (LEDs), excellent mobilities contribute to the efficient capture of nonequilibrium charge carriers to rare nonradiative centres. Moreover, the lack of bound excitons weakens the competition of desired radiative over undesired nonradiative recombination. Here we also report a perovskite mixed material, one comprised of a series of differently quantum-size-tuned grains, that funnels photoexcitations to the lowest-bandgap light-emitter in the mixture. The materials function as charge carrier concentrators, ensuring that radiative recombination successfully outcompetes trapping and hence nonradiative recombination. We use the new material to build devices that exhibit an external quantum efficiency (EQE) of 8.8% and a radiance of 80 Wsr-1m-2. These represent the brightest and most efficient solution processed near-infrared LEDs to date. Here we show that, by concentrating photoexcited states into a small subpopulation of radiative domains, one can achieve a high quantum yield even at low excitation intensities. We tailor the composition of quasi-2D perovskites to direct the energy transfer into the lowest-bandgap minority phase, and to do so faster than it is lost to non-radiative centres. The new material exhibits 60% photoluminescence quantum yield at excitation intensities as low as 1.8 mW/cm2, yielding a ratio of quantum yield to excitation intensity of 0.3 cm2/mW; this represents a two-orders of magnitude decrease in the excitation power required to reach high efficiency compared to the best prior reports. Using this strategy, we report LEDs with EQEs of 7.4% and a high luminescence of 8400 cd/m2.

Electrically-pumped lasing remains an elusive grand challenge for the organic and thin film electronics community. Recently, hybrid organic-inorganic perovskites have emerged as promising gain media for tunable, solution-processed semiconductor lasers, sparking interest in the use of these materials for an eventual diode laser. This talk will focus on recent progress toward this goal, including the demonstration of optically-pumped, continuous-wave lasing from methylammonium lead iodide (MAPbI3) as well as an investigation into the nature of quantum efficiency roll-off in MAPbI3 light emitting diodes operated at current densities exceeding 300 A/cm2.

Color-pure green emission is essential to realize next-generation vivid displays. Recently, solution-processed OIHPs are attracting increasing attention because of their narrow emission, and potential to be fabricated energy-efficient and low-cost in lighting and display applications. However, the perovskite light emitting diodes (LEDs) that approach Rec. 2020 standard green emission with a maximum current efficiency ≥15 cd/A have not been achieved by far. Here, we present ultrapure green LEDs based on quantum confined colloidal perovskite emitters. A spin-coated thin film of two dimensional (2D) perovskites demonstrates a high absolute photoluminescence quantum efficiency (PLQE ~ 94%). The resultant perovskite LEDs show a maximum current efficiency >20 cd/A by using a composite emission layer of colloidal 2D perovskites and poly(methyl methacrylate). As compared to Rec. 2020 standard color gamut, the green emission shows >97% color saturation in the 1931 CIE color space. We present ultra-flexible perovskite LEDs with a bending curvature radius of 2 mm by using a 50 μm thin polyimide substrate. We further demonstrate a high-efficiency large-area (30 mm2) device without compromising in the device performance. These devices show ultimate potential to realize low-cost, large-scale fabrication of the ultra-pure green LEDs for the next-generation of displays.

Organic-inorganic halide perovskites have attracted considerable attention in the past few years because of their remarkable performance in optoelectronic devices. However, long-term stability of the materials and devices remains the biggest challenge for realistic implementation of perovskite solar cells. Although significant efforts have been carried out on the causes of degradation at the device level, yet few measurements have been made at the surface analytical level to reveal the degradation mechanisms. I’ll present our work on the effects of environmental factors, such as O2, water, and light, on the perovskite layer by monitoring the intrinsic electronic structure and compositional changes in different aging tests. This work contributes in developing better understanding of the degradation mechanisms to improve the overall stability of perovskite light emitting diodes and solar cells.

We introduce a simple and low-cost approach, drop-coating method, for preparation of in-situ selfassembled perovskite nanocrystals for efficient light-emitting diodes. The PL spectrum of the self-assembled NFPI₄ nanocrystals thin film prepared by the drop-coating method shows blue shift compared with that of the typical NFPI₄ thin film prepared by spin-coating method. In addition, the PL spectra of these self-assembled nanocrystals are tuned from 765 nm to 725 nm by changing usage amounts of the perovskite precursor solution. More importantly, efficient light-emitting diodes with EQEs up to 6.8% are achieved based on these self-assembled NFPI₄ nanocrystals.

Inorganic perovskite quantum dots (P-QDs) is a new kind of optoelectronic materials in recent years. Because the high quantum yield (QY), the narrow full width at half-maximum (FWHM) and spectrum tenability of novel P-QDs, making them have more potential on the display application. However, P-QDs not only have poor water resistance and heat resistance, but also easily exchange halogen ions to cause wavelength variations. Therefore, the above problems must be solved before use. In this study, red and green P-QDs were synthesized by thermal injection method and then mixed with polymethyl methacrylate (PMMA) in different ratios. Controlling the P-QD concentrations and the thickness of the fluorescent films to form white light. The results show that the fluorescent film can avoid the ion exchange reaction effectively. Moreover, the CIE of P-QD/PMMA device locates at (0.29, 0.31), and the NTSC and sRGB are 131 and 183 %, respectively.

The mobile display market is strongly shifting towards AMOLED technology which enables curved and flexible displays. Therefore, the demand for highly efficient OLED emitters to reduce power consumption and increase display resolution at the same time is growing. There are efficient green and red OLED emitters in mass production already, but there is no efficient blue counterpart. CYNORA´s approach to provide efficient blue OLED emitters is based on thermally activated delayed fluorescence technology. TADF emitter systems allow for an efficiency increase of up to four times compared to conventional fluorescent systems by utilizing both triplet and singlet excitons for the emission of light. At the same time, they maintain deep blue emission, i.e. CIEy < 0.2. Herein, we review our recent progress on TADF emitters, reaching 20% EQE at 1000 nits in deep blue OLED devices (< 460 nm peak wavelength) together with reasonable LT97 values. The performance of these new blue TADF emitters is now in the range of commercial requirements for blue emitters in OLED displays.

In this paper, we had designed the hole transport layer of the new composite skeleton structure having a high energy band gap, high triplet energy and charge mobility. And we proposed a new structure to incorporate carbazole on thiophene to solve energy band gap, triplet energy and charge mobility. The structures and properties of the synthesized compounds were characterized by NMR, fluorescence spectroscopy, triplet energy, charge mobility. As a result of NMR measurement, it was confirmed that when analyzing the integrated type with the position where the measured peak is displayed, it agrees with the structure of hole transport materials. The emission characteristics of the hole transport layer material showed absorption characteristics at 401nm and 377nm, respectively, and exhibited emission characteristics in the range of 460nm and 435nm. respectively, The triplet energy was 2.78 eV and mobility was 7.12X10^-6 cm²/Vs.

In this paper, we adopt solution/evaporation hybrid processes to fabricate white organic light emitting diodes (WOLED) with a light-emitting area of 1.5 cm * 1.5 cm. The hole injection layer (PEDOT:PSS), p-type doped hole transport layer (NPB:F4-TCNQ), and emitting layer (UBH-215:UBD-07:DBP) are coated using the solution process while the electron transport layer (TPBI), LiF, and Al are coated through vacuum thermal evaporation. The light-emitting layer is a fluorescent material (UBH-215 as host) that combines the blue fluorescent material UBD-07 and the red fluorescent material DBP for a dual band light-emitting diodes. We found that if the red DBP doping concentration is too high, the overall emitting color tends toward reddish, and the luminance efficiency decreases. For WOLEDs whose red DBP doping concentration is 0.25%, the luminance reaches 192 cd/m², and the current efficiency 0.94 cd/A at 9V voltage.

Introducing a hole injection layer between the ITO and emitting layer can enhance both the luminance and efficiency of a WOLED. In addition to the hole injection layer, it is found that inserting p-type doped HTL (NPB:F4-TCNQ) between HIL and EML using the spin- coating method can also improve luminance and efficiency. Furthermore, by optimizing and adjusting the dopant ratio and thickness of p-type doped HTL, the luminance reaches 393.1 cd/m2, the current efficiency reaches 1.32 cd/A under 9V voltage, and the OLED lifetime (half-value period) increases from the original 0.8 hours to 2 hours.

We are using organic small molecules as absorbing material to investigate coherent perfect absorption in layered thin-film structures. Therefore we realize strongly asymmetric resonator structures with a high optical quality dielectric distributed Bragg reflector and thermally evaporated wedged organic materials on top. We investigate the optical properties of these structures systematically by selective optical pumping and probing of the structure. By shifting the samples along the wedge, we demonstrate how relations of phase and amplitude of all waves can be tuned to achieve coherent perfect absorption. Thus almost all incident radiation dissipates in the thin organic absorbing layer. Furthermore, we show how these wedged structures on a high-quality reflective dielectric mirror can be used to determine optical dispersion relations of absorbing materials in a broad spectral range. This novel approach does not require any specific a priori knowledge on the absorbing film.

A series of 2,6-bis-styryl-4H-pyran-4-ylidene fragment containing glassy organic compounds with chemically stable bonding of amorphous phase promoting bulky triphenyl moieties through piperazine structural fragment (DWK-T dyes) in a form of 2-(5,5,5-triphenylpentyl)piperazin-1-yl)styryl)-substituent have been synthesized and investigated as the potential gain medium component for organic solid state laser applications. Physical properties of the dyes vary and are mostly depending from the other styryl-substituent attached to the 4H-pyran-4-ylidene backbone fragment in 6-position. Thermal stability of synthesized dyes is above 312°C with the glass transitions from 97°C to 109°C. Obtained neat spin-cast films based on these compounds exhibit photoluminescence with λ_max in range from 672 nm to 695 nm, ASE λ_max from 690 nm to 704 nm with ASE threshold values in range from 327 μJ/cm² to 1091 μJ/cm². Parameters are mostly influenced by the electron affinities of various 4-substituents in 6-styryl-fragment. The proposed synthetic approach could be useful for obtaining stable covalently bonded bulky triphenyl group containing glassy dyes while the synthetic design allows to acquire different non-symmetric 2,6-bis-styryl-4H-pyran-4-ylidene fragment containing compounds for infra-red light-emitting and light amplification systems.

In this work, OLEDs based on a new modified polymer PMC 300* (as emissive layer: EML) were manufactured with the structure ITO/PEDOT:PSS/Polymer (PMC 300*)/LiF or PFN/Al. This new polymer PMC 300*: Poly[(Benzo[c][1,2,5]thiadiazole-4,7-diylbis(9,9-dimethyl-9H-fluorene-7,2-diyl))-3,3-diyl(1-(3- (trifluoromethyl)phenyl)-2-oxindole)], is a modified version of PF-1 polymer that was synthesized and used previously in our group for non-linear optical properties and in OLED devices. The CF3 additional group on PMC 300* showed an improved electroluminescence and current efficiency on OLED devices. PF-1 and PMC 300* polymers have a fluorescence quantum yield (FLQY) of approximately 1. Film formation of the hole injection layer (HIL) and the EML were made by spin coating and subsequently evaporating LiF (or PFN by spin coating) and Al as cathode. Polymer films show a very low roughness (~ 1-2 nm), as most of the polymers used in OLEDs. Due to PMC 300* excellent properties like high solubility, very high QY, high conjugation and mechanical characteristics, OLEDs based on this new modified polymer (with emission in green-yellow wavelengths) showed luminances up to 1937 cd/m², high current efficiencies of 35 cd/A and a maximum external quantum efficiency (EQE_max) of 2.6 %. Additionally, preliminary tests of flexible OLEDs by using this polymer are currently carrying out, results are promising.

Hyperfluorescence^TM, exhibiting 100% energy-to-light conversion efficiency, a sharp yet brighter emission spectrum, and excellent CIE coordinate coverage, is the ultimate 4th generation OLED technology. With our unique approach to material design and device optimization, Kyulux will provide our customers with industry leading fluorophores in all colors. Together, we will deliver unparalleled picture quality and energy efficiency to OLED display market.

As OLED applications increase, so do the demands on properties of the component materials, active layers and devices. The development of flexible OLEDs, a popular future OLED application, require better understanding and control of the mechanical properties of OLED materials and interaction with polymer substrates. Fabrication costs, use of extended classes of materials and the need for large surface area applications drives interest in solution-phase processing techniques; requiring OLEDs with different solubilities and glass transition temperatures than traditional vacuum deposited layers and device stacks. In this era of designing for multiple property requirements, computational techniques can provide important capability to screen new materials and understand the relationship between chemical structure and dependent properties. In this work we show automated molecular dynamics (MD) simulation workflows that efficiently and accurately calculate mechanical and physical properties of OLED materials.