This PDF file contains the front matter associated with SPIE Proceedings Volume 11808, including the Title Page, Copyright information, and Table of Contents

OLEDs are thin-film devices consisting of multilayers of organic thin films sandwiched between a metal and an ITO electrodes. Because of the different refractive indices of the layers in the thin film stack, different optical modes are trapped in the device. In this talk, we will first discuss the physics of these optical modes and describe techniques to characterize them. We will then describe how to use various photonic structures to maximize the light output and manipulate these optical modes to control the polarization as well as directionality to achieve beam shaping.

The largest need in organic electronic devices is a universal method to produce micro- to nano-scale features for devices from semiconducting polymers cheaply, and at scale. We recently developed a solution method to optically pattern conjugated polymers with resolution that exceeds the linear Abbe diffraction limit. We examine the relationship between optical write intensity, write speed, and write wavelength on the resulting pattern fidelity. Finite element modeling reveals that nearly all patterning occurs as a result of local heating and superlinear resolution is a result of a highly non-linear dissolution rate for the polymer as a function of temperature. This result is general to any conjugated polymer. We used this new technique to fabricate P3HT/F4TCNQ nanowires We also demonstrate that a P3HT nanowires can be doped and de-doped from solution without changing the dimension of the wire.

Cavity effects play an important role in determining the out-coupling efficiency of an OLED. By fabricating OLEDs on corrugated substrates, the waveguide and SPP modes can be extracted by diffraction. However, corrugation does not always lead to an enhancement in out-coupling efficiency due to the reduction of the electrode reflectance and hence the cavity effects. Based on the results of our rigorous couple-wave analysis (RCWA) simulation, we found that the cavity effects can be partially recovered using a low index Teflon layer inserted between the ITO anode and the substrate due to the enhancement of the reflectance of the corrugated electrodes. To verify the simulation results, we fabricated corrugated OLEDs having a low-index Teflon interlayer with an EQE of 36%, which is 29% higher than an optimized planar OLED. By experimentally measuring the OLED air mode dispersion, we confirm the cavity emission of a corrugated OLED is enhanced by the low index layer.

Light emitting diodes (LEDs) with directional and polarized light emission have many photonic applications, and beam shaping of these devices is fundamentally challenging because they are Lambertian light sources. In this work, using organic and perovskite LEDs (PeLEDs) for demonstrations, by selectively diffracting the TE waveguide mode while suppressing other optical modes in a nanostructured LED, we first demonstrated highly directional light emission from a full-area organic LED with a small divergence angle less than 3°, and a TE to TM polarization extinction ratio of 13. The highly selective diffraction of only the TE waveguide mode is possible due to the planarization of the device stack by thermal evaporation and solution processing. Using this strategy, we further demonstrated directional and polarized emission from a perovskite LED having a current efficiency 2.6 times compared to the reference planar device.

Lighting today is expected to be light weighted, flexible, highly efficient, non-expensive and fabricated in an environment friendly way. Organic light emitting diodes (OLEDs) meet all of these requirements and can be applied using inexpensive and roll-to-roll compatible printing techniques. This work demonstrates the ultrasonic spray coating (USSC) of polyethylenimine (PEI) and polyethylenimine(ethoxylated) (PEIE) as electron injection/transport layer (EIL/ETL) for OLEDs. This high-end printing technique employs ultrasonic atomization to break down a liquid into a spray of homogeneous small (20 µm) droplets. The PEI(E) layer was optimised using USSC and subjected to a complete morphological and electro-optical characterisation. For all manufactured devices current and voltage characteristics and luminous performances were obtained. This study confirms the versatility of USSC and the suitability of PEI(E) as excellent EIL/ETL for OLEDs and paves the way towards fully printed devices.

OLEDs consisting of Au-NPs sandwiched between anode and hole injection layer, and close to an active layer inside PEDOT:PSS is fabricated by Ultrasonic Spray Coating (USSC). Optimized surface coverage of Au-NPs on ITO facilitates efficient charge injection and an optimized position of the Au-NPs away from the active layer accelerates the radiative recombination. Obtained results indicate that USSC could effortlessly tune the surface coverage and the vertical position of the Au-NPs to enhance the OLED’s efficacy. This paves the way for the fabrication of large area, high efficient OLEDs with USSC.

Human-interactive displays (HIDs) facilitate the visualization of sensible information such as touch, smell, and sound and have attracted significant interest owing to their potential in emerging IoT-connected wearable electronics. Furthermore, the visualization of phenomena that is rarely sensible, such as magnetic fields, ultrasonic waves, and odorless toxic gases or liquids, can further broaden the utilization of HIDs. Field-induced electroluminescence (EL) of either organic or inorganic fluorescent materials under alternating current (AC) has been extensively studied and its unique device architecture in which an emitting layer is separated with an insulator from electrode offers a new platform for designing and developing emerging HIDs. Here, we present various sensory and extra-sensory interactive displays based on AC EL.

We characterize the magneto photocurrent (MPC) response in polycrystalline tetracene-based diodes and magneto photoluminescence of the tetracene film and attribute the initially decreasing and then increasing MPC responses to the feature of the singlet fission (SF) reaction. The SF reaction in polycrystalline tetracene active layer is more evident when the device was irradiated with the short wavelength of irradiation. This observation indicates a possible route to utilize the excess exciting energy for the generation of extra excited states (triplet) to contribute the higher photocurrent. Additionally, through the measurement of magneto electroluminescence of tetracene-based diodes operated under the forward bias regime, we are able to characterize the reaction of triplet-triplet annihilation (TTA) to harvest the energy from triplet to singlet excitons in part contribute the emission of fluorescence especially in the high current density and low temperature regime.

The search for alternative transparent electrodes to the commonly used indium tin oxide (ITO) in optoelectronic devices has led to solution-based approaches based on inkjet printing. As an additive manufacturing technique that allows drops to be positioned only where necessary, inkjet printing shows reduced waste of starting material compared to other methods such as spin coating. As a result, functional materials can be both coated and structured without the need for masks or lithographic pre-patterning of the substrate. For this contribution, we utilized a particle-free silver ink to produce a transparent electrode by inkjet printing. After printing, the silver ions were reduced to metallic silver by an argon plasma. The process takes place at low temperatures (ca. 40 – 50°C), making it suitable for use with flexible substrates, which are often temperature-sensitive. The printed silver layers show good electrical conductivity and optical transmittance, with a crystalline grain structure being formed and maintained during the metallization process. This structure forms a self-organized nanometer-size grid, whose structure allows light to pass through. Due to its nano-structured property, the haze of the electrode was investigated using a simple experimental setup based on a light source shining through the electrode and analyzing the size of the projected pattern. Such qualitative assessment can be a useful indication of the quality of the electrode and we provide details on how to replicate this setup. The final electrodes were implemented in solution-processed OLEDs, which showed bright luminance and overall low haze compared to ITO-based reference devices.

In this paper we introduce a new light emitting device where phosphorescent emitters are intentionally coupled to the surface plasmon mode of a nearby metal electrode for decay rate enhancement. This energy is subsequently converted to photons in free space via a nanoparticle-based out-coupling scheme allowing us to harvest both efficiency and stability gains. Compared to a reference OLED based on conventional device design, our new architecture achieves a two-fold increase in operational stability at the same brightness while simultaneously outcoupling 8% of photons from the device.

Organic light-emitting diodes (OLEDs) offer unique properties such as large-area emission, compatibility with flexible substrates, tuning of emitted spectrum, and structuring into high-density arrays. This makes OLEDs attractive for biomedical applications like on-chip sensing or wearable health monitoring and, more recently, also to control the activity of neurons through a method called optogenetics. So far, most light sources used in optogenetics provide limited spatial resolution. In this contribution, we present micropatterned OLEDs that are capable of precisely controlling neuronal activity in Drosophila melanogaster (fruit fly) larvae. The OLEDs provide highly confined light stimuli to individual abdominal segments, which allows precise activation and inhibition of sensory input in larvae. Our work demonstrates the advantages of OLED technology for neuroscience and provides prospects for future integration of OLEDs in implants.

In this study, we will present two topics. One is a systematic in silico material design for thermally activated delayed fluorescence (TADF) with very fast reverse intersystem crossing (RISC). The other is our recently-developed multiscale charge transport simulation based on the combination of quantum chemical calculations, molecular dynamics simulations, and kinetic Monte Carlo simulations. Using the simulation, we will investigate what happens in the emitter layer of organic light-emitting diodes.

The efficiency of OLEDs is fundamentally determined by the spin of excited state electrons. We have previously shown, using a new class of emissive molecules, carbene-metal-amides (CMA), an unusual emission pathway based on spin-state inter-conversion - intramolecular rotation induces a shift in the relative energies of the first excited singlet and triplet states, leading to extremely efficient singlet-triplet state interconversion and photoemission. In our recent work, we report solution-processed dual-dopant polymer LEDs, in which highly efficient electroluminescence occurs via an intermolecular energy transfer from CMAs to a fluorescent emitter. With electroluminescence from the simple fluorophore, we obtained record EQEs of >20% in these devices. Photophysical measurements indicate that ultrafast inter-fluorophore energy transfer occurs with near-unity efficiency. They preserve the relative colour purity of simple fluorophores, potential for energy-efficient printable electronics.

An approach to enhance the lifetime of a phosphorescent organic light-emitting diode (PHOLED) with a solutionprocessed hole-transport layer (HTL) by employing energy transfer from an exciplex to a phosphorescent emitter is presented. Using the structure of solution-coated Poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4′-(N-(4-secbutylphenyl) diphenylamine)] (TFB) as a HTL and vacuum-deposited 4,4′-Bis(carbazol-9-yl)biphenyl (CBP) as a host provides a suitable situation for the formation of exciplex between CBP and TFB because energy gap between the LUMO level of CBP and the HOMO level of TFB becomes much smaller than the HOMO-LUMO gap of CBP or TFB. As the PHOLED emission is solely from the phosphorescence, the intermediate exciplex state rapidly transfers its energy to the dopant triplet. Since singlet-excited state of exciplex requires much lower energy than singlet-excited state of the host, driving voltage for PHOLEDs using exciplex–triplet energy transfer (ExTET) is lower than conventional, leading to longer device lifetime. The results show that the electroluminescence half-life (LT50) of fabricated device with the structure of HTL TFB and host CBP in which exciplex can form between CBP and TFB is about 5785 h (for an initial luminance of 1000 cd m−2). On the other hand, in the other fabricated devices with the same structure and just mixing TFB with other materials with deeper HOMO level, where the ability to form exciplex between TFB and CBP is suppressed, the device lifetime is significantly shorter. To the best of our knowledge, it is the first time that ExTET is obtained in a hybrid structure involving solution-coated and vacuum-deposited layers.

Despite extensive research on near-infrared organic light-emitting diodes (OLEDs), the external quantum efficiency (EQE) of these devices are far lower than devices with visible light emission. Recently, doublet fluorescent emission from organic radicals has emerged as a new route to more efficient light-emitting devices than those using established non-radical organic emitters. Charge recombination in radical devices results in doublet excitons with nanosecond emission and avoids the efficiency limit usually associated with singlets and triplets. For the application of the organic radicals to near-infrared electroluminescence, the novel near-infrared radical emitter showing around 800 nm emission was designed. Using the organic radical, not only higher than 5% EQE was attained but also the efficiency roll-off and operational lifetime were substantially improved in addition to decreasing turn-on and driving voltage significantly.

Spin is a quantum property fundamental to the charge-light conversion process in optoelectronic devices. Organic materials offer unique opportunities to exploit spin due to their long coherence and lifetimes. The hyperfine interaction, which dominates the spin-dependent recombination processes of these materials, can be chemically tuned on a molecular level while retaining the large-scale fabrication techniques of those materials. To date, this property has been treated monolithically, characterized by a single value across a device. We utilize optical microscopy to spatially resolve the magnetoluminescence effect of an OLED and show the intra-device variation of this spin property reaches nearly 30%. We explore how the variation of this property changes with the operating bias to probe the underlying spin physics and show that these molecular-scale interactions are spatially correlated microscopically over the device.

Molecules that undergo thermally activated delayed fluorescence (TADF) represent an important class of systems for the design of efficient organic lighting (OLEDS) because they utilize both singlet and triplet excitons for electrically-generated light emission. Most molecules of this type have considerable charge transfer (CT) character as this is known to result in nearly degenerate singlet and triplet energies. Another important consequence of this CT character is that the TADF efficiency as well as the emission wavelength and color purity are highly sensitive to the polarity of the local environment. Here we present data demonstrating the effect of local polarity on the fluorescence intermittency (blinking) of single TADF molecules isolated in a series of host matrices of varying dielectric constants. The on and off times of the fluorescence of single chromophores are shown to be highly sensitive to local polarity and are used to model the dynamics of singlet-triplet crossing.

Much effort has been directed at understanding organic light-emitting device (OLED) efficiency and the role of bimolecular quenching in efficiency roll-off. Quenching is less widely discussed at low-bias, where populations are reduced. Here, we describe lock-in-based photoluminescence measurements on working phosphorescent OLEDs to demonstrate that this assumption is not generally valid, and that significant exciton-polaron quenching is present even prior to turn-on. Exciton-polaron quenching arises with holes accumulated due to spontaneous orientation polarization in the electron transport layer. This low-bias quenching is found to strongly determine maximum achievable efficiency, suggesting a need to refine materials selection and device design rules.

We present our recent efforts for the design of high-colour purity multiresonant TADF emitters. We will present examples ranging from near-UV to orange emitters. We demonstrate how it is possible to accurately predict their photophysical properties and how computations guide molecular design, producing high-performance OLEDs.

Long-lived room temperature ‘phosphorescence’ from organic molecular crystals has attracted great attention owing to potential applications in organic electronics, information storage, and biotechnologies. The features of the persistent luminescence strongly depend on the electronic properties of the individual molecules, and on their molecular packing in the crystal lattice. Here, a new strategy is developed by rationally designing phosphors incorporating and combining for the first time a bridge for sigma-conjugation and a moiety for H-bond-directed supramolecular self-assembly. The molecular crystals exhibit room temperature ‘phosphorescence’ quantum yields that reach up to 20% and lifetimes up to 520 ms. This study provides a promising strategy for the development of molecular crystals exhibiting efficient long-lived room temperature persistent luminescence.

Multiple resonance (MR) effect of boron and nitrogen/oxygen atoms induces the localization of the HOMO and LUMO on different atoms and minimizes their bonding/anti-bonding character; the resulting non-bonding molecular orbitals minimize the vibronic coupling and vibrational relaxation in the material, allowing the realization of an extremely sharp emission band and high PLQY. Moreover, the significant localization of the HOMO and LUMO reduces the energy gap between the S1 and T1 states, promoting the reverse intersystem crossing and thermally activated delayed fluorescence (TADF). Here, we present recent achievements in MR-TADF materials, construction of new core structures, and device applications.

Thermally-activated delayed fluorescence (TADF) emitters can in principle allow for 100% internal quantum efficiency of organic light-emitting diodes (OLEDs), because the initially formed electron-hole pairs in the non-emissive triplet state can be efficiently converted into emissive singlets by reverse intersystem crossing. Moreover, TADF emitters offer the advantage to align them such that their optical transition dipole moments (TDMs) lie preferentially in the film plane. In this talk, we address the question which factors control the orientation of TADF emitters. Specifically, we discuss how guest-host interactions may be used to influence this parameter and propose an interplay of different factors being responsible. We infer that emitter orientation is mainly governed by the molecular shape of the TADF molecule itself and by the physical properties of the host. Ref: B.A. Naqvi et al., Frontiers in Chemistry 8, 750 (2020)

Organic materials are good absorbers for optical filters and good emitters for OLEDs, largely due to their high oscillator strengths. However, this comes at the cost of broad spectral linewidths, which limits the usefulness of absorptive filters and restricts colour purity in displays. Interference-based structures offer narrower spectra but show an intrinsic and often substantial angle dependence. Here, we overcome these limitations by combining the concepts of absorption and interference. Introducing absorbers into a microcavity leads to a coupled polariton state that inherits the low dispersion of the material exciton and the narrow linewidth of the cavity mode and thus enables line-filters with record spectral discrimination and angular stability (e.g., FWHM <50meV/11nm @538nm central wavelength, angle shift <26meV/6nm @80° tilt). Using a similar concept, we show efficient OLEDs with angle-independent, narrowband emission (EQE >10%, FWHM <20nm, angle shift <10nm @60° tilt).

In this talk, we will firstly present a strategy to realize deep blue TADF OLEDs with the EQE of 28% and CIE y value of 0.09 by narrowing the emission spectrum of blue TADF emitters along with high horizontal emitting dipole orientation. Secondly we will present deep blue OLEDs utilizing TTA process based on anthracene derivatives. For blue-emitting anthracene derivatives, the theoretical maximum contribution of TTA to emissive singlet excitons is considered to be 15%, which is insufficient for high-efficiency fluorescent devices. In this study, we realised a TTA contribution of nearly 25% using an anthracene derivative, breaking the theoretical limit. As a result, efficient deep-blue TTA fluorescent devices were developed, which exhibited maximum external quantum efficiencies of 10.2%. A theoretical model will be presented to explain the experimental results considering both the TTA and RISC to a singlet state from a high level triplet state formed by the TTA process.

To date, the development of organic light-emitting diode (OLED) materials has been primarily based on a combination of chemical intuition and trial-and-error experimentation. The approach is often expensive and time-consuming, let alone in most instances fails to offer new materials leading to higher efficiencies. Data-driven approaches have emerged as a powerful tool to accelerate the design and discovery of novel materials with multifunctional properties for next generation OLED technologies. Virtual high-throughput methods assisted by machine learning (ML) enable a broad screening of chemical space to predict material properties and suggest new candidates for OLEDs. In order to build reliable predictive ML models for OLED materials, it is required to create and manage a high volume of data which not only maintain high accuracy but also properly assess the complexity of materials chemistry in the OLED space. Active learning (AL) is among several strategies developed to face the challenge in both materials science and life science applications, where the data management in large-scale becomes a main bottleneck. Here, we present a workflow that efficiently combines AL with atomic-scale simulations to reliably predict optoelectronic properties of OLED materials. This study provides a robust and validated framework to account for multiple parameters that simultaneously influence OLED performance. Results of this work pave the way for a fundamental understanding of optoelectronic performance of emergent layers from a molecular perspective, and further screen candidate materials with superior efficiencies before laborious simulations, synthesis, and device fabrication.

In this work, we describe an atomistic-scale modeling and simulation scheme to virtually screen both host materials and light emitters used in OLEDs while assessing molecular orientations in film. The work also demonstrates the ability to predict wavelength-dependent refractive indices from atomistic-scale up to achieve this goal. These findings would provide valuable guidelines for the development of new material architectures with superior optical loss properties as well as improved outcoupling efficiencies at the device level.

In this presentation, we will discuss our continuing efforts on the design, synthesis and characterization of novel platinum and palladium complexes for displays and lighting applications. The photo-physics, electrochemistry, electroluminescent properties and operational stability of these novel metal complexes, including deep blue narrowband emitters and amber emitting phosphorescent molecular aggregates, will be discussed. The rational molecular design enables us to develop cyclometalated metal complexes with both photon-to-photon (in thin film) and electron-to-photon (in device settings) conversion efficiency close to 100% for OLED applications. Our approaches to achieve high efficiency white OLED will be also included.

This presentation video was recorded for the SPIE Optics + Photonics 2021 symposium.

Organic light-emitting diodes (OLEDs) are a promising light-emitting technology useful for various display applications. Despite great progress in this field, there is an ongoing challenge to realize high-performance blue OLEDs with efficiency, good color purity, and device lifetime. Here, we report pure-blue (CIEx,y color coordinates of [0.13, 0.16]) OLEDs with high-efficiency (external quantum efficiency of 32 % at 1000 cd m^–2), narrow-emission (full-width half maximum of 19 nm), and good stability (LT95 of 18 hours at an initial luminance of 1000 cd m^–2). The design is based on a two-unit stacked tandem hyperfluorescence (HF)-OLED with an improved singlet-excited energy transfer process from a sky-blue TADF assistant dopant (AD) (HDT-1) to a pure-blue terminal emitter (TE) (v-DABNA). Furthermore, the effect of the dopant concentration of terminal emitter on the device performance of hyperfluorescence OLEDs is studied. The device shows a better color purity when dopant concentration is increased. On the other hand, new hyperfluorescence OLEDs are fabricated, in which v-DABNA is replaced by DABNA-2 and dopant concentration is kept to be 0.5 %. Such device shows a lengthened device stability of LT95 of 26 h at an initial luminance of 1000 cd m^-2

Quasi-2D perovskite is considered as a promising candidate for blue perovskite light emitting diode (PeLEDs). However, the wide distribution of low-order phases, inefficient energy transfer, and defects/traps increase the non-radiative recombination, further aggravating PeLED external quantum efficiency (EQE). We demonstrate a unique quasi-2D perovskite with low-order phase suppression and defect passivation by incorporating a 2D perovskite and an excess ammonium salt into the quasi-2D perovskite. By optimizing the new quasi-2D perovskites, we achieve blue PeLEDs with brightness 1765 cd m-2, EQE 7.51%, low turn-on voltage 3.07 V, and long operation lifetime 3961 sec without any shift in electroluminescent spectra.

This presentation video was recorded for the SPIE Optics + Photonics 2021 Symposium.

Organic–inorganic hybrid perovskites such as methylammonium lead halide (CH3NH3PbI3) have been employed in photoelectronic device applications such as light-emitting diodes, solar cells, field-effect transistors, and photodetectors. Combining ultraviolet photoemission spectroscopy(UPS), X-ray photoemission spectroscopy (XPS), atomic force microscopy(AFM), X-ray diffraction measurements (XRD), and device fabrication and characterization, we performed a systematic investigation on the correlation of energy level alignment, film growth and molecular orientation of a number of interfaces and their modifications in photodetectors based on CH₃NH₃PbI₃ and FA_0.4MA_0.6PbI₃.

We present variable-size circular micro methylammonium lead iodide PeLEDs and systematically examine their performance in moderate and high current density regimes. We demonstrate the beneficial influence of device downscaling on the internal heat generation and its positive impact on lifetime. For micron size glass-based devices with external quantum efficiencies (EQE) of around 5.5 %, we achieve a T50 > 5 h at 1000 mA·cm-2 at room temperature. The scaling-down approach and device architecture optimizations allowed for pulsed driving of the PeLEDs as short as 250 ns, reaching exceptionally large current densities above 5 kA·cm-2 and radiance values above 30000 W·m-2·sr-1.

This presentation video was recorded for the SPIE Optics + Photonics 2021 symposium.

In this study, we investigated the methods for prolonged lifetime in the CsPbX3 (X: Cl, Br, I) structured perovskite materials. First, the changes in structural and optical properties were compared by doping Ni in the CsPbBr3 quantum dots (QDs). The steady-state photoluminescence (PL) intensity of Ni-doped QDs shows 3.8 times increase comparing with undoped QDs. CsPbBr3 without nickel had a quantum efficiency of only 56.7 %, whereas CsPbBr3 doped with nickel had a quantum efficiency of 82.9 %. It was found that the doped divalent element acts as a defect in the perovskite structure, reducing the recombination rate of electrons and holes. After 48 hours UV-light irradiation, PL intensity of CsPbBr3 decreased about 70 % while that of Ni-substituted CsPbBr3 QDs decreased only 18 %, indicating the prolonged stability against UV-light irradiation. Furthermore, Ni-substituted CsPbBr3 QDs shows higher stability against temperature and moisture. These results confirmed that Ni substitution method is effective to increase the stability of CsPbX3 QDs. Second, we used sulfuroleylamine (S-OLA) complex which was utilized to etch the defect-rich surface of the CsPbI3 QDs and then self-assembly to form a matrix outside the CsPbI3 QDs protected the QDs from environmental moisture and solar irradiation. The PL intensity of the CsPbI3 QDs increased by 21% of its initial value. There was a significant increase in the colloidal stability of the CsPbI3 QDs. The introduction of S-OLA induced the recovery of the lost photoluminescence of the nonluminous aged CsPbI3 QDs with time to 95% of that of the fresh QDs. Furthermore, the PL was maintained for one month. The increase in the stability and PL intensity are critical for realizing high-performance perovskite-QD-based devices. In this study, we investigated the methods for prolonged lifetime in the CsPbX3 (X: Cl, Br, I) structured perovskite materials. First, the changes in structural and optical properties were compared by doping Ni in the CsPbBr3 quantum dots (QDs). It was found that the doped divalent element acts as a defect in the perovskite structure, reducing the recombination rate of electrons and holes. Ni-substituted CsPbBr3 QDs shows higher stability against temperature and moisture. These results confirmed that Ni substitution method is effective to increase the stability of CsPbX3 QDs. Second, we used sulfuroleylamine (S-OLA) complex which was utilized to etch the defect-rich surface of the CsPbI3 QDs and then self-assembly to form a matrix outside the CsPbI3 QDs protected the QDs from environmental moisture and solar irradiation. The introduction of S-OLA induced the recovery of the lost photoluminescence of the nonluminous aged CsPbI3 QDs with time to 95% of that of the fresh QDs.

Halide-based perovskite materials have been spotlighted in light-emitting diodes and perovskite solar cells applications due to their excellent optical and electrical characteristics. In particular, excellent film quality of perovskite with defect passivation is required to obtain highly efficient and stable perovskite optoelectronic devices. However, lots of undesired trap sites by defect sites such as voids, pinholes, grain boundaries and under-coordinated ions in surface of film can be formed in solution-processed perovskite films, reducing the device performance and operational stability of perovskite devices. Here, we demonstrate efficient perovskite optoelectronic devices by incorporating poly(fluorene-phenylene)-based anionic conjugated polyelectrolytes (CPEs).

This presentation video was recorded for the SPIE Optics + Photonics 2021 symposium.

Perovskite light-emitting diodes (PeLEDs) have shown great potential for next-generation display and solid-state lighting applications. In the related field of perovskite solar cells, preventing the conversion of the photovoltaically active black phase (α-phase) into the less desirable yellow phase (δ-phase) is of critical importance for achieving efficient and stable solar cells based on formamidinium lead iodide (FAPbI₃) perovskite. Similar issues related to phase stability are expected to occur in PeLEDs, leading to reduced operational stability and the formation of additional electronic traps. In this work, we introduce an additive, sulfobetaine 10 (SFB-10), into the FAPbI₃ perovskite for α-phase stabilization. The SFB-10 incorporated perovskite films show enhanced crystallinity, reduced defect density and improved α-phase stability, leading to high-performance PeLEDs with external quantum efficiencies exceeding 16%, and T₉₀ (the time for radiance to decrease to 90% of its initial value) of over 1000 s at 200 mA cm^-2 in air, offering a comparable performance to some of the most stable PeLEDs reported to date. This work may contribute to the development of stable perovskite light-emitting diodes.

In this work we will discuss high temperature macroscopic quantum coherent effects, specifically superfluorescence in hybrid perovskites.

The vast chemical and processing universe of emerging halide perovskite materials can be overwhelming to traditional research practices. The sheer scale of the design problem and the emergent nature of many phenomena, including highly nonequilibrium thin film processing, complex solution-to-solid phase transformation can be overwhelming for traditional trial-and-error investigations. Solving such a complex problem would benefit from a robot-in-the-loop strategy that can accelerate many of the manual tasks as well as reduce cost and waste generation and support implementation of artificial intelligence. We present the RoboMapper, our recent effort to leverage robotic automation towards accelerating parameter space exploration and establishment of formulation-structure-property relationships with orders of magnitude enhancement in research efficiency. We will demonstrate formulation, printing and characterization of halide perovskites towards the aim of accelerating research workflows.

Continuous-wave (CW) lasing and amplified spontaneous emission (ASE) in 3D perovskite films has only been demonstrated at cryogenic temperatures. To understand the temperature limits of CW ASE, we investigate the carrier dynamics and determine the bimolecular and Auger recombination constants from 80 K up to 290 K in phase-stable triple cation perovskites. The bimolecular rate coefficient decreases with increasing temperature, whereas the Auger rate coefficient remains unchanged from cryogenic to room temperature. Above 250 K, at the ASE threshold carrier density, Auger recombination dominates the carrier dynamics and thus limits the lasing operation. At lower temperatures, below 250 K, the dominant effects leading to an increased ASE threshold with temperature are the decrease in the radiative recombination rate and the increased energy dilution of the charge carriers. Both of these effects reduce the rate of spontaneous emission into the ASE band.

This presentation will present our recent studies on spin-orbital coupling (SOC) effects of light-emitting properties in organic and perovskite materials. In general, SOC generates two fundamental outcomes: (i) spin flipping in the absence of orbital momentum and (ii) Rashba effects in the existence of orbital momentum. The former and latter play a critical role in controlling light-emitting properties. In organic materials, this presentation will discuss the new mechanism of forming SOC from amorphous charge-transfer states in the absence of heavy-metal complex structures. Essentially, a charge-transfer state simultaneously possesses internally-interacting electrical dipole and spin dipole, providing the fundamental possibility to generate an electric-magnetic coupling phenomenon functioning as an artificially-formed SOC, towards realizing a thermally activated delayed fluorescence (TADF) in organic molecules. In perovskites, this presentation will discuss the orbit-orbit interaction

In optoelectronic devices, the function and performance depends crucially on the proper alignment of the energy level landscape throughout the device, allowing for efficient charge transport across the various interfaces. In perovskites it turned out that these interfaces can be rather complex. On the one hand, interface dipoles and band bending occur. But more importantly, the perovskite composition and formation can be significantly influenced by chemical reactions taking place at these interfaces. In this talk I will summarize our recent work on a variety of metal-oxides in which we use photoelectron spectroscopy to analyze which components are responsible for the strong interface chemistry. For this, we looked at a variety of different perovskites (i.e. organic vs. inorganic ones, I vs. Br, etc.) as well as the individual perovskite precursors. Overall, I will show how photoelectron spectroscopy measurements can help to probe and understand the processes going on at these vario

This presentation video was recorded for the SPIE Optics + Photonics 2021 symposium.

Highly stable perovskite quantum dots (PeQDs) are developed using excess Zn precursor and trioctylphosphine‐oxide (TOPO). They not only have high quantum efficiency and sharp full width at half maximum values (15–30 nm) but also have improved long‐term stability at high temperature. They have EQE (%) and current efficiency (Cd A−1) of (7.12%, 9.93 Cd A−1) for red, (6.06%, 32.5 Cd A−1) for green, and (0.56%, 0.88 Cd A−1) for blue‐emitting devices, respectively. Also, a new hole-transporting material, poly-2-(9Hcarbazol-9-yl)-5-(4-vinylphenyl)-5H-benzo[b]carbazole (PBCZCZ), was developed for perovskite light-emitting diodes (PeLEDs). The EQE of the green PeLEDs using PBCZCZ was about 2.5 times higher and that of the sky-blue PeLEDs was about 3 times higher than the device made with the commercial HTL of PVK. The operational device lifetimes of the green and sky-blue PeLEDs made with PBCZCZ were about 4.1 and 4.8 times higher than the PVK-containing device.

Semiconductor nanocrystal core/shell quantum dots (QDs) have successfully extended their original fundamental research into many practical applications. But core/shell QDs may still not satisfying enough in practical applications because of the existence of photoblinking, multi-exponential PL decay behavior, and Förster resonance energy transfer (FRET) between QDs. Herein we report an approach to synthesize a series of alloyed core/shell QDs by a “low-temperature injection and high-temperature growth” precisely controlled method. By probing shell-thickness dependent performance, ZnCdSe-based core/shell QDs not only with nonblinking but also single photoluminescence decay channel and suppressed FRET have been successfully prepared. As emitters, such ZnCdSe- based QLEDs exhibit high external quantum efficiencies, low-efficiency roll-off at high current density, and long operational lifetime.

While the narrow emission spectrum and high quantum yield of quantum dots (QDs) is desirable for light emitting devices (LEDs), the mechanisms that limit electroluminescent QDLED stability must be understood before they can be used in high brightness applications. The deep energy levels of Cd-based QDs allow for relatively easy electron injection but comparably difficult hole injection, resulting in an imbalance of charge carriers in the emission layer (EML) that can reduce efficiency via non-radiative recombination. The incorporation of a multi-component hole transport layer (HTL) consisting of materials with sequentially deeper highest occupied molecular orbital (HOMO) energy levels in a cascading HTL (CHTL) architecture has been shown to improve QDLED lifetime by 20x while also enhancing luminous efficiency. Prompt and delayed electrical and spectroscopic measurements indicate that the CHTL structure shifts excessive hole accumulation away from the QD/HTL interface, resulting in less degradation of the HTL in contact with the QD EML, and reduces leakage current by blocking electron transport to the anode. The trade-off between exciton density in the HTL vs. QDLED efficiency and stability highlights the importance of the HTL in long-term device performance.

Perovskites, widely-known for their promise in solar photovoltaics, also show promise in the realization of light-emitting diodes. Multiple classes of materials and emission wavelengths have now exceeded EQEs of 20%. Much effort has been invested in achieving charge transport layers that invest efficiently into these devices. Brightnesses are now reaching interesting levels for applications in information display. A key gating item is to advance further the understanding of degradation mechanisms, and to lever this understanding to extend operating lifetimes, just as the OLED community did two decades ago. I will review progress and open questions.

Previously we proposed a highly effective extraction-enhancing OLED display pixel structure based on embedding the top-emitting OLED inside a 3D reflective bank structure covered with a patterned high-index filler. For top-emitting OLED using transparent top electrode (e.g., TCO like ITO), optical simulation indicated that the optical out-coupling efficiency can be enhanced by nearly 2.8 times (e.g., from 24% to 68%). Here in this work, through optical simulation and design, we show that the overall optical out-coupling efficiency of such 3D OLED pixel configuration can be further enhanced by forming the distributed Brag reflector (DBR) between the top-emitting OLED and the high-index filler and strengthening the microcavity effect of the top-emitting OLED.

Development and characterization of novel OLED materials by traditional computational approaches are challenging owing to the complex factors that simultaneously influence the device performance. In this work, we will provide an overview of generative OLED materials discovery using the latest deep neural network formalism, and show an illustrative example to design novel OLED hole-transport materials. The outcome of the work will demonstrate the value of systematic and fundamental understanding of structure-property correlations that can lead to rational design of smart OLEDs with higher efficiency.