This PDF file contains the front matter associated with SPIE Proceedings Volume 11093, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Even after over 30 years’ development and successful commercialization of organic light emitting diodes (OLEDs), very interesting and important innovations have occurred in OLEDs in recent years. Recently reported thermally activated delayed fluorescence (TADF) materials, utilizing intra- and inter-molecular charge transfer processes upon excitation, is an example which can harvest triplet excitons or exciplexes to light. Another example is the demonstration of external quantum efficiencies (EQEs) of over 30%, approaching almost 40% without any external light extraction structures. This high efficiency was realized based on the development of highly oriented phosphorescent or TADF emitters parallel to the substrate (horizontal direction), combined with advanced device structures. Improving efficiency is important because it is directly related to the reduction of power consumption and device lifetime. In this presentation, recent development of high efficiency OLEDs based on phosphorescent, TADF and fluorescent emitters will be discussed. We will show that EQEs over 50% is achievable without any extra light extracting structure and over 80% with light extraction structures if OLEDs are fabricated using organic semiconductors with the low refractive index and fully horizontal emitting dipoles. Finally, we will also discuss on the possibility of realizing high efficiency blue OLEDs with long lifetime, one of the most important issues in OLEDs.

The development of high efficient and color pure blue emitting materials is most important issue. In this presentation, I will report various design stratergies for the development of high efficient and color pure blue emitting materials by using phosphorescence, TADF, and fluoresence with TTA. Especially, the new blue phosphorescent materials showed over 30 %, blue TADF materials showed over 27 % , and blue fluorescence materials showed over 14%.

During the last few years, the phenomenon of thermally activated delayed fluorescence (TADF) finds more and more applications in numerous fields of technology, especially in organic light emitting diodes (OLED) giving rise to variously shaped and flexible optoelectronic devices and displays. Further development of products using OLED technology requires emitters exhibiting deep-blue TADF with relatively short emission lifetimes and high chemical stability. The state-of-the-art pure organic TADF emitters comprise donor and acceptor fragments separated spatially. This enables very small gap between the lowest singlet and triplet excited states of charge-transfer (CT) character. However, as these states differ only by multiplicity, the transition between them is forbidden by the selection rules. According to the current understanding of TADF mechanism, the efficient conversion of nonradiative triplet excitons to the emissive singlet ones occurs when a locally excited triplet state (3LE) is energetically close to the ¹CT and ³CT states. The photophysical principles described above work very well for design of efficient yellow, green, and sky-blue TADF materials. To achieve deep-blue TADF, the emitter should comprise highly energetic CT and ³LE states, which is a challenging requirement. To face this problem we investigated two approaches of increasing excited states’ energies: (i) reduction of conjugation of the acceptor fragment by its deplanarization and (ii) introduction of electron-releasing substituents in the acceptor fragment. 2-Phenyl-s-triazine and 9,10- dihydro-9,9-dimethylacridine were selected as acceptor and donors fragments, respectively. Our results show that both approaches efficiently increase energies of the CT and acceptor ³LE states, maintaining the rate constant of reverse intersystem crossing in the 10⁵–10⁶ s^–1 range. This presentation will focus on details of the above mentioned investigations including characteristics of the OLED devices.

Efficient doublet emission from radical materials and devices Feng Li State Key Laboratory of Supramolecular Structure and Materials, College of Chemistry, Jilin University, Qianjin Avenue 2699, Changchun, 130012, P. R. China (E-mail address: lifeng01@jlu.edu.cn) A new kind of OLEDs based on radicals, in which the emission comes from a spin doublet rather than from a singlet or triplet exciton was developed. The emission process is spin-allowed in these systems, usefully, the classical triplet-limiting efficiency for OLEDs is circumvented for doublets [1]. After continually optimizing materials and devices [2,3], a D-A type luminescent radical emitter, TTM-3NCz, was used as the emitter of an OLED with a maximum external quantum efficiency of 27 %—the highest reported value for deep-red and infrared LEDs [4]. There is only one family of room-temperature luminescent radicals, triphenylmethyl radicals, so far. We synthesized a new stable room-temperature luminescent radical, (N-carbazolyl)bis(2,4,6-tirchlorophenyl)methyl radical (CzBTM), which is beyond the family of triphenylmethyl radicals. A new family of stable luminescent radicals based on CzBTM is anticipated [5]. [1] Q.M. Peng, A. Obolda, M. Zhang, F. Li, Organic Light-Emitting Diodes Using a Neutral pi Radical as Emitter: The Emission from a Doublet, Angew. Chem.-Int. Edit., 54 (2015) 7091-7095. [2] Y. Gao, W. Xu, H. Ma, A. Obolda, W. Yan, S. Dong, M. Zhang, F. Li, Novel Luminescent Benzimidazole-Substituent Tris(2,4,6-trichlorophenyl)methyl Radicals: Photophysics, Stability, and Highly Efficient Red-Orange Electroluminescence, Chem. Mat., 29 (2017) 6733-6739. [3] A. Obolda, X. Ai, M. Zhang, F. Li, Up to 100% Formation Ratio of Doublet Exciton in Deep-Red Organic Light-Emitting Diodes Based on Neutral pi-Radical, ACS applied materials & interfaces, 8 (2016) 35472-35478. [4] X. Ai, E.W. Evans, S. Dong, A.J. Gillett, H. Guo, Y. Chen, T.J.H. Hele, R.H. Friend, F. Li, Efficient radical-based light-emitting diodes with doublet emission, Nature, 563 (2018) 536-540. [5] X. Ai, Y. Chen, Y. Feng, F. Li, A Stable Room-Temperature Luminescent Biphenylmethyl Radical, Angew. Chem.-Int. Edit., 57 (2018) 2869-2873.

Organic materials that exhibit thermally activated delayed fluorescence (TADF) are attractive materials for realizing high efficiency OLEDs. A tremendous amount of tailor-made 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 of using exciplex that simply involves intermolecular charge transfer between physically blended electron donor and acceptor molecules. This is because the exciplex-based systems can realize relatively small ΔEST since the electron and hole are located 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. 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, the developments of exciplex-forming systems for achieving high-efficiency and high stability OLED devices are prospective. In this conference, our updated results of new efficient exciplex systems, and exciplex-hosted fluorescent and phosphorescent OLEDs with high efficiency and high stability will be reported.

Intra-molecular CT states play an important role in the photo-physical processes and eventual device performances of organic electroluminescent materials such as organic thermally activated delayed florescence (TADF) and radical emitters. For organic TADF emitters, we have shed light on how the energy levels and excitation characters of intra-molecular CT states impact electronic-structure parameters such as singlet-triplet energy gap, spin-orbit coupling, transition dipole moment, and thus reverse intersystem crossing and radiative decay processes. For organic radical emitters, we have designed donor-acceptor neutral radicals based on the electron-poor perchlorotriphenylmethyl (PTM) or tris(2,4,6-trichlorophenyl)methyl (TTM) radical moiety combined with different electron-rich groups. Experimental and quantum-chemical studies demonstrate that the molecules do not follow the Aufbau principle: The Singly Occupied Molecular Orbital (SOMO), mainly localized on the PTM [TTM] segment, is found to lie below the Highest (doubly) Occupied Molecular Orbital (HOMO), mainly localized on the donor segment. Such the non-Aufbau behavior in the organic radical emitters is resulted from a high-energy CT state. These donor-acceptor radicals provide a remarkable combination of strong D1-to-D0 emission yield (up to 54%) and high photo-stability (e.g., the half-lives reach up to several months under pulsed UV laser irradiation). Organic light-emitting diodes (OLEDs) based on a radical emitter show near-infrared (NIR) emission with a high maximal external quantum efficiency of 4.0 %.

Polyelectrolytes have been proposed as the charge injection/extraction layers for organic electronics for a long time. These layers have the advantage of orthogonal solvent processing, but suffer from large electrical resistance. In this talk, I will describe recent work that shows that greatly superior results are obtained when the polyelectrolytes get chemically doped to give what we call heavily charge-doped, self-compensated polymers. These materials can be designed through careful selection of semiconductor core, counter-ion, and spectator-ion, to achieve any desired work function between 5.8 eV to 2.4 eV, sufficient to create ohmic hole, and electron, injection contact at will, to almost any semiconductor. I will also explain how we can at the same time achieve ambient processability for even the ultra work function materials, opening an unprecedented path for ambient solution deposition.

Despite the advances, the exploitation of the full utility of organic electroluminescence devices (OLEDs) has been retarded by the short lifetime of blue-emitting devices. The poor longevity originates from irreversible, chemical degradation of emitting layers. However, the molecular mechanism by which degradation initiates has yet to be fully elucidated to date. My group proposed that the degradation involves exciton-mediated formation of polaron pairs (radical ion pairs) between wide hosts and dopants. To examine this hypothesis, we performed mechanistic studies with employing chemical techniques. Electrochemical studies predicted a thermodynamic allowance for the occurrence of reductive electron transfer from a dopant to host exciton to form a polaron pair involving positive polaron of a dopant and a negative polaron of host. Photoinduced EPR spectroscopy was employed to monitor the generation of the polaron pair. In particular, nanosecond laser photolysis experiments were successful in monitoring the annihilation of the polaron pair that occurred in the Marcus-inverted region of electron transfer. The annihilation competed with chemical degradation, and our analyses of degradation byproducts indicated an occurrence of CN bond breakage of both host and dopant molecules. Finally, a linear correlation was found between device lifetimes and rate constants for the annihilation of the polaron pair. This result supports our mechanism which involves the exciton-mediated generation of labile radical ion species. Further, our findings demonstrate the importance of controlling exciton-induced electron transfer within an emitting layer, and provide novel molecular strategies to improved device longevity.

Low work-function electrodes are required for efficient electron injection into semiconductor devices. However, electrodes with work functions shallower than ca. 4 eV suffer from fundamental incompatibility with ambient processing. Here, we provide an elegent solution to resolve this paradox using latent electron donors. Based on di- and higher-valent anions, including oxalate, carbonate and sulfite, which are stable in their native solution state, they provide surprisingly shallow donor energies when isolated as dehydrated ion clusters in organic matrices to electron-dope shallow electron-affinity semiconductor cores and reach previously inaccessible work functions as small as 2.4 eV. These shallow anion donors thus provide universal n-doping of most semiconductors of interest from ambient processable formulations. We observe spontaneous electron transfer to the semiconductor core upon removal of the stabilizing water molecules, or upon photo sensitization of the semiconductor core, or its hole sensitization by injection from opposite contact, while solvation serendipitously protects the anion from from premature doping and destruction. Using the recently developed self-compensated, doped polymer platform ω-trimethylammonioalkyl-functionalized polyfluorene, and silver as cathode, we demonstrated doping of the electron injection layer to provide unprecedented ohmic electron injection into the shallow electron-affinity organic semiconductor benchmark, poly(9,9-bis(4-octylphenyl)fluorene-2,7-diyl). We also show that higher performance can be realized generally with these highly-doped electron injection/extraction layers in organic solar cells and white light-emitting diodes, opening new device design latitudes.

Efficiency roll-off and intrinsic luminance degradation are two of the primary limitations of organic light-emitting devices (OLEDs). While both phenomena have been studied separately in detail, they are rarely considered together. Previous analyses of OLED degradation have largely neglected changes in efficiency roll-off and bimolecular quenching, and the magnitude of these changes and their impact on device lifetime remains unclear. We present experimental and modeling results to quantify the magnitude of these changes, which we find range from ~2% to above 10% in magnitude and increase in importance at high brightness or in devices with significant exciton-exciton annihilation.

Organic semiconductors are promising for the development of many applications including in solid state lighting, flexible displays and organic-based lasing. However, a critical factor limiting their utility is their inherently low stability relative to inorganic materials. This instability causes organic molecules to be susceptible to oxygen damage in an irreversible process known as photo-bleaching. This effect necessitates the development of highly impermeable encapsulation strategies and limits device lifetimes. Plasmonic engineering offers one avenue to alter the decay rates of fluorophores and modify the emission from single molecules and thin films. Here, we demonstrate that by carefully engineering the properties of ultra-thin gold films to match the plasmon with the emission of organic molecules a photostability enhancement of more than 60-fold can be achieved. As an example, we successfully demonstrated that OPPV-13, an oligomer of poly [2-methoxy-5(2'-ethylhexyloxy)-1,4-phenylene]vinylene, deposited on 2 nm thick Au substrates retains its fluorescence under constant illumination in ambient conditions for 45 minutes compared to less than 2 minutes when it is deposited on glass substrates. The underlying mechanism of this remarkable enhanced photostability is probed using a variety of microscopy-based tools and extensions to other opto-electronic materials are described.

Additives such as solvents, nano particles and ionic lquids were found to be very effective in improving PSS:PEDOT polymer properties. However, small molecules have strong tendency to diffuse, especially at working condition when temperature is higher. Dangling structure copolymer, such as Nafion and Flemion and/or their chemical derivatives may be better replacements. PSS:PEDOT:Flemion was 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. Flemion copolymer was found to form strong link to both PEDOT and PSS chains. While, causing similar effect on PEDOT polymer chains as pfi (Nafion) copolymer, increasing PSS monomer-monomer bending angle and repulsion among monomers it does not cause strong phase separation. DFT simulation indicates, Flemion can form strong hydrogen bond complex with PSS:PEDOT, and lower their HOMO energy as well. Flemion may be candidate as an additive to manipulate PEDOT concentration profile in selforganized PSS:PEDOT:pfi film.

Biomaterials offers opportunities to design compact and coherent light sources applicable to biological sensing and imaging applications due to the biocompatibility of the devices. To date, conventional techniques have been adopted to design biological light sources such as planar microcavity laser, microspheres, distributed feedback lasers and random lasers (RLs). Among those RLs are easy to fabricate by the random distribution of scatterers in a gain medium to achieve amplified gain and coherent lasing. Here, we report a fully biocompatible light source exhibiting RLs and low threshold amplified spontaneous emission (ASE). A favorable combination of a silk inverse opal (SIO) with the inherent disorder and sodium fluorescein a biocompatible optical gain incorporated into a silk protein film induces random cavities. An inverse opal of proper diameter with optical gain forms high Q random cavities due to refractive index modulation induced by the structural imperfections, which induced gain enhancement to show low threshold ASE and distinguishable coherent RLs spikes. Also, high surface-to-volume ratio and the trait of amplification of the SIO led to highly efficient chemosensing to detect the HCl vapor. Furthermore, SIO can have a form of microparticles. Lasing from the SIO powder under a plant tissue is demonstrated as a proof-of-concept experiment for applicability of the prepared RL under biological surfaces as a tissue engineering biological device. Our finding opens upon new ways to develop compact size bio-lasers.

A large band-edge offset at organic/inorganic interfaces and imbalance in charge carrier mobilities of conjugated polymers limits an efficient charge injection and recombination in polymer light-emitting diodes (PLEDs). In this talk, I will discuss how the electrochemical doping of conjugated polymers with ultra-trace (< 1 wt%) electrochemical doping agents (EDAs) can significantly improve charge injection and balance, hence enhancing the recombination and device performance. In particular, I will highlight a dramatic reduction of turn-on voltages for current and luminance achieved in the single-layer PLED devices up to 1.2um-thick. I will also show other advantages of the ultra-trace electrochemical doping which allows fabrication of large-area devices with homogeneous electroluminescence emission. Our work provides a simple but highly feasible strategy for developing high-quality efficient light applications fully compatible with printing technologies.

Here, we demonstrate anion-exchange red perovskite QDs CsPb(Br/I)3 from pristine CsPbBr3 using ammonium-iodine salts, long alkyl-based oleylammonium iodide (OAM-I) and aryl-based aniline hydoroiodide (An-HI), for use in highly efficient light-emitting devices (LEDs). The anion-exchange CsPb(Br/I)3 films exhibit a strong red-shift in their of photoluminescence (PL) spectrum from the green emission at 508 nm in the case of the pristine QDs to one in the deep-red region at 649 nm owing to the replacement of Br– anions by I–¬ anions in the perovskite QDs. LEDs formed using the anion-exchange CsPb(Br/I)3 based on OAM-I show an remarkable high EQE of more than 20% as well as high color purity, with the Commission Internationale de l'Eclairage (CIE) at (0.72, 0.28), which completely cover BT.2020 color gamut. Similarly, the LEDs formed using the QDs based on An-HI show a peak EQE of 14.1% and CIE coordinates of (0.71, 0.28). Further, they exhibit longer operational stability as compared to that of LEDs formed using the OAM-I-based CsPb(Br/I)3.

The low efficiency of fluorescent blue OLED pixels remains one of the top issues for OLED panel makers despite the success that OLED displays have had on the market in the last decade. Recent progress on the TADF technology, however, has shown this technology´s potential to finally deliver high-efficiency deep-blue materials that also have enough stability for OLED panels. CYNORA has already shown that the customer specifications for color and efficiency can be reached and the lifetime is in the final development stage. We were able to reach these results with two separate TADF approaches, the self-emitting and the co-emitting (or hyper) approach. In this paper, we will show some of the requirements for the TADF emitter that are necessary to achieve good results in the co-emitting approach. We will discuss the theoretical requirements to achieve good energy transfer from a TADF emitter to a fluorescent emitter. We will also show device results that confirm the required deep-blue color of the TADF emitter for efficient hyper-fluorescent devices. And we will also give an update on our latest results where we have achieved more than 20% EQE (external quantum efficiency) at deep-blue colors with a CIEy 1931 coordinate of ≤0.15.

Organic light-emitting diode (OLED) technology is promising for next-generation displays and lighting. On the other hand, hybrid perovskite light-emitting diodes (PLED) have recently emerged. In this study, we incorporated metal halide hybrid perovskites as host or carrier transport layers into OLEDs with the aim of obtaining device performance higher than that of existing OLEDs and PLEDs. Hybrid perovskite films can be prepared with a simple method, such as spin coating or vacuum deposition, similarly to organic film fabrication. This is because of their excellent self-organization nature. Even in spin-coated and vacuum-deposited hybrid perovskite films, carrier mobilities are very high compared with organic films used for OLEDs. This is associated with inorganic metal halide frameworks formed through films. Additionally, more singlet excitons than usual can be generated in an organic emitter as a result of energy transfer from a hybrid perovskite portion. This energy transfer also lead to good operational durability under continuous operation. By taking these advantages, we demonstrated extremely high performance from OLEDs with hybrid perovskites. We believe that this sort of organic/perovskite hybrid device architectures can be a new technology, which enables the fabrication of more efficient and stable LEDs with lower voltages at a lower cost in the future.

ZnO-based nanoparticles (NPs) are widely used as the electron transport layers (ETLs) for quantum dot light-emitting diodes (QLEDs) because of their advantages of high electron mobility and appropriate energy levels. However, QLEDs with ZnO ETLs suffer from unbalanced charge injection and interfacial exciton quenching. To address these issues, the ZnMgO NPs are doped by polyvinylpyrrolidone (PVP), which improves the morphology, reduces the conductivity and decreases the surface quenching sites of ZnMgO ETLs. As a consequence, QLEDs with ZnMgO:PVP hybrid ETLs exhibit a high current efficiency (CE) of 56.70 cd/A and a peak EQE of 13.36%, which are about 1.33-fold higher than those of the devices with ZnMgO ETLs. In addition, the ZnMgO NPs are effectively densified by doping PVP. Because of the improved compactness, the hybrid ETL can even withstand the plasma damage during indium-tin-oxide (ITO) sputtering, which thus enables the fabrication of transparent QLEDs. We also show that the formation of microfilaments can be eliminated by replacing the problematic ZnMgO with more compact ZnMgO:PVP composite. The developed ZnMgO:PVP composite, with improved compactness, tunable conductivity and reduced quenching sites, could be the ideal ETLs for efficient bottom-emission and transparent QLEDs.

Poor light extraction efficiency from OLEDs is among the leading problems facing the science and commercialization of OLEDs. The light outcoupling ~1/2n2, where n is the refractive index of the organic emitting layer, and is only 17-20% for planar OLEDs. The remaining light is waveguided in the organic +ITO layers (>30%), waveguided in the substrate, or lost to plasmonic excitation in the cathode that can be very severe (>40%) for thin ETLs. To enhance outcoupling we investigate the light emission from periodically corrugated OLEDs where the OLED stack is grown conformally on a periodic textured substrate [1]. The corrugation diffracts wave-guided modes to the air cone, thereby increasing outcoupling, but no simulations have predicted enhancements or optimal corrugations. We utilize rigorous scattering matrix simulations solving Maxwell’s equations in Fourier space, for all polarizations. We find the corrugated OLEDS display a remarkable light outcoupling of 60-70%, approaching the targeted value of 70% in the solid-state lighting road-map. We find optimal corrugation pitch of 0.75-3 microns with only a small roll off for larger pitch. The optimal corrugation heights exceed 150 nm. There is a marked decrease in plasmonic losses. Corrugations induce strong diffraction of light into the air cone. We also find that adding a microlens on the air-substrate interface can increase by a further ~5-10%. We compare simulations with experimental results [1].Supported by DOE-EERE [1] C. Hippola et al, Adv. Optical Materials 6, 1701244 (2018).

Quasi-2D Ruddlesden-Popper halide perovskites with a large exciton binding energy, self-assembled quantum wells and high quantum yield draw attention for optoelectronic device applications. Thin films of these quasi-2D perovskites consist of a mixture of domains having different dimensionality, allowing energy funneling from lower-dimensional nanosheets (narrower bandgap domains) to three-dimensional nanocrystals (wide bandgap domains). Here, the quality of quasi-2D perovskite (PEA)2(FA)3Pb4Br13 is controlled by solution engineering. Grazing-incidence wide-angle X-ray scattering (GIWAXS) measurements were conducted to study the crystal orientation, and transient absorption spectroscopy (TAS) measurements were conducted to study the charge carrier dynamics. Our data show that the highly oriented 2D crystals have a faster energy transfer to the low bandgap regime (< 0.5 ps) compared to less oriented films. High-performance LEDs can be realized with these 2D films. Finally, amplified spontaneous emission is achieved with an ultralow threshold of 4.16 μJ/cm2 and distributed feedback lasers are realized. Our results show that it is important to control the morphology and spatial domain distribution of the quasi-2D films to achieve efficient energy transfer, which is a critical requirement for optoelectronic devices.

Halide Perovskites have shown potential for high-performance cost-effective optoelectronics. Previous work in this field has been primarily focused on pristine perovskites. We discovered that perovskites in form of composites can sometime outperform the pure perovskites with improved material stability. In this talk, I will focus on the correlation between the crystal phases and the microscopic structures, as well as the favorable physical properties we have observed in composite perovskites.

The exceptional luminescence properties of colloidal quantum dots (QDs) make them advantageous for use as an electroluminescent material in light emitting devices (QDLEDs). Drastic improvements in the performance of QDLEDs have been achieved through the use of inorganic electron transport layers and organic hole transport layers (HTLs), yet the electroluminescence stability of QDLEDs remains insufficient for commercial applications. To address the issue of QDLED stability, significant work has been done to reduce charge imbalance and Auger recombination in the QDs which arises from the large energy level mismatch between the valence band of the QD and the highest occupied molecular orbital (HOMO) of the HTL. This work identifies morphological stability within QDLEDs as an additional degradation mechanism limiting device stability. Interaction between the HTL and surface roughness of the underlying layers appears to be a critical parameter to address in QDLED design. Studies of QDLEDs using electrical measurements and electroluminescence imaging elucidate upon the role that morphological stability plays in the degradation of electroluminescent QDLEDs.

Material deposition rate during device fabrication is known to influence film morphology. Using the archetypical phosphorescent organic light-emitting devices (PhOLED) hole transport material 4,4′-Bis(carbazol-9-yl)biphenyl, the influence of the deposition rate on hole transport layer (HTL) morphology and its effect on the electroluminescence stability of PhOLEDs is investigated. Photoluminescence measurements show that films deposited at lower deposition rates tend to have a shorter exciton lifetime and a higher exciton stability. Atomic force microscopy measurements reveal that films deposited at various deposition rates develop different morphological features over time. More notably, films deposited at lower deposition rates exhibit increased surface roughness and the presence of larger crystalline regions when compared to their counterparts deposited at the higher rates when tested a few days after film deposition, indicating that the lower deposition rate leads to increased structural order in film morphology. We also found that using a lower deposition rate during HTL fabrication can lead to an increase in the electroluminescence stability of PhOLEDs. The increased stability can be attributed to the higher morphological or structural order and shorter exciton lifetime in them, hence a decreased susceptibility to exciton-induced degradation. These findings show direct correlations between material deposition rate, HTL morphology and PhOLED electroluminescence performance.