Performance Of Organic Light-emitting Diodes Research Articles

Blue Organic Light Emitting Diode Materials based on Different Light-emitting Groups

Abstract: Organic light emitting diode (OLED) is a device that uses organic semiconductor materials to emit light under the action of an electric field. Compared with traditional luminescent materials, they have the advantages of good softness, low-temperature resistance, wider field of vision and low energy consumption, and have been widely used in the field of display and lighting in recent years. In addition, compared with red and green light-emitting materials, the maximum external quantum efficiency of blue-light materials-based devices is high, but the CIE coordinate performance is poor and the blue emission is difficult to achieve high efficiency and high color purity at the same time. Researchers continue to design new molecular structures in order to synthesize new high-efficiency blue light materials. It is found that different molecular structures have different effects on the performance of OLED devices. In the design and synthesis of blue-light materials, various light-emitting groups are often used to regulate the stability, singlet-third-line state of the target molecule energy level difference, excited state lifetime, aggregation state structure, electricity luminescent color and its OLED performance, etc. The introduction of different lightemitting groups into the blue light material greatly improves the performance of the material. This paper mainly reviews the research status of blue organic electroluminescent materials in the past five years from different molecular structures, further discusses the photoelectric properties of each compound and the properties of devices based on this material, and briefly analyzes the advantages of molecular design and device production. And finally discusses the improvement methods of blue OLED light-emitting materials in order to provide a reference for future research.

Enhanced performance of organic light-emitting diodes by integrating quasi-periodic micro-nano structures

To integrate a quasi-periodic micro-nano structure (PMS) to the organic light-emitting devices (OLEDs) is an efficient way to enhance the performance of OLEDs. In this paper, the PMS prepared by the phase separation of Polystyrene and Poly (methyl methacrylate) was integrated to the OLEDs with the structures of Glass/PMS/Ag (30 nm)/MoO3 (5 nm)/(NPB) (40 nm)/(Alq3) (60 nm)/LiF (0.5 nm)/Al (150 nm). The maximum luminance intensity and external quantum efficiency increased to 10700 cd/m2 and 1.11 %, which is 48 % and 44 % higher than that of 7209 cd/m2 and 0.77 % of the planar reference device. The enhanced performance of OLEDs was ascribed to the attenuation of surface plasmon polariton loss caused by the PMS, which was testified by the Finite-Difference Time-Domain (FDTD) simulation. The PMS was also transferred to the hole transfer layer (PEDOT: PSS) of OLEDs by nano-imprinting lithography with the structure of Glass/(ITO) (100 nm)/PEDOT: PSS (100 nm) (with PMS)/NPB (10 nm)/Alq3 (50 nm)/LiF (0.5 nm)/Al (100 nm). The performance was also improved by the optimized PMS and the light out-coupling efficiency increased to about 49.5 %, which is much higher than that of 28.8 % in the OLEDs with PMS Ag anode and 20 % in the planar reference devices. This suggests that the PMS can improve the OLED device performance regardless of the functional layer in which the PMS is integrated.

Investigations on exciton recombination and annihilation in TmPyPB-ETL OLEDs using magnetic field effects.

Although the effect of the electron transport layer (ETL) material TmPyPb on the electroluminescence performance of organic light-emitting diodes (OLEDs) has been extensively studied, the process of TmPyPb regulating exciton recombination and annihilation within the device is still unclear. Here, we fabricated devices of various TmPyPb thicknesses with and without ETL. Subsequently, we measured the magneto-electroluminescence (MEL) of these devices. Specifically, at the same luminance, the triplet-charge annihilation (TQA) process is more likely to occur as the thickness of TmPyPb increases, resulting in a decrease in the maximum luminance of devices. Due to electron leakage and exciton recombination region moving towards the cathode, leading to a decrease in luminance efficiency at first and then an enhancement with an increase in the thickness of TmPyPb. Furthermore, at room temperature, the application of a large bias voltage suppresses singlet fission (SF) processes by modulating the dissociation of singlet polaron pairs (PPS) and the concentration of triplet exciton (T1). This leads to the conversion of SF to the TQA process. At low temperatures, the bias voltage and temperature can regulate the concentration and lifetime of PPS and T1. Therefore, as the temperature decreases, the transition of SF → TQA → triplet-triplet annihilation (TTA) and TQA coexistence → TTA process occurs. Moreover, MEL responses of the TmPyPb-ETL device show a W-linear pattern owing to the combined effect of the hyperfine interaction (HFI) and Zeeman splitting at 145 K. Accordingly, we explored the electroluminescence (EL) performance of TmPyPB-ETL OLEDs and investigated the evolution of SF, TQA, and TTA processes using MEL. Our study revealed the effect of exciton recombination and annihilation in OLEDs with varying thicknesses of TmPyPb.

Electroluminescent Performances of Solution-processed Phosphorescent Organic Light-emitting Diodes Based on Cascade Energy Transfer of Ternary Blends

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Solution-processed triphenylethylene-fluorene fluorochromes toward deep-blue organic light-emitting diodes: benefits of preventing radical formation

High band exciton is easily trapped and quenched by the defect structure in wide bandgap light-emitting conjugated materials (LCMs), which is harmful to the performance and stability of deep-blue organic light-emitting diodes (OLEDs).

Multiple Fusion Strategy for High-Performance Yellow OLEDs with Full Width at Half Maximums Down to 23nm and External Quantum Efficiencies up to 37.4.

The pursuit of ideal narrowband yellow multiple resonance (MR) emitters is hampered by the mutual constraints of effective spectral redshift and maintaining a small full width at half maximum (FWHM) value. Here, a novel multiple fusion molecular design strategy is reported to break this trade-off. Compared with the selected narrowband parent core, the specific multiple MR effects in target molecules can simultaneously extend the π-conjugation length, increase the rigidity of the structure, and reduce the vibrational frequency. Proof-of-the-concept emitters BN-DICz and DBN-ICz show bright yellowish green to yellow emissions in dilute toluene solutions with peaks at 533-542nm and extremely small FWHMs of ≤20nm. Notably, BN-DICz-based electroluminescent device exhibits excellent efficiencies of 37.4%, 136.6cd A-1 , and 119.2lm W-1 with an FWHM of merely 23nm, representing the best performance for yellow MR organic light-emitting diodes.

A Study on Varying the Number of Fluorene Units in 2, 1, 3‐Benzothiadiazole‐Containing Oligomers and the Effect on OLED Performance and Stability

AbstractSolution‐processing has the potential to reduce the cost and energy requirements in the fabrication of organic light‐emitting diode (OLED) devices. In non‐doped emissive layers, polymers are commonly used but often suffer from batch‐to‐batch variation. Oligomers, which have precise molecular structures, avoid this problem but maintain the favourable film‐forming properties that polymers possess. We present three benzothiadiazole‐containing fluorene‐based oligomers, BT‐F32, BT‐F42 and BT‐F52, which have terfluorene, quaterfluorene and pentafluorene arms, respectively, attached to a benzothiadiazole core. The materials show very high photoluminescence quantum yields, with BT‐F42 exhibiting the highest PLQY of 0.96 in the thin film. Although there is little change in the electroluminescence spectra, the oligomer size influences device performance. BT‐F32 had an external quantum efficiency of 1.9 % and high luminance whilst BT‐F42 reached an external quantum efficiency of 2.3 %. Furthermore, the stability of the OLED devices was evaluated and showed that the device lifetime decays with increasing molecular length.

Correlating Exciton Dynamics of Thermally Activated Delayed-Fluorescence Emitters to Efficiency Roll-Off in OLEDs

Physical parameters, such as decay rates and photoluminescence (PL) quantum efficiencies, associated with thermally activated delayed fluorescence (TADF) emitters play a critical role in determining the performance of organic light-emitting diodes (OLEDs). Herein, we investigate the impact of TADF decay rates and PL quantum efficiencies on external quantum efficiency (EQE) roll-off. Our analysis reveals that a high EQE with suppressed efficiency roll-off in TADF OLEDs can be achieved by shortening the delayed lifetime with an increasing delayed contribution or by shortening the prompt lifetime with increasing prompt contribution simultaneously. We further show that TADF compounds with long delayed and/or prompt lifetimes can give rise to multiple spin cycling and subsequently result in significant exciton quenching and efficiency roll-off in OLEDs. These results provide universal selection criteria for TADF emitters in OLEDs to concurrently achieve a high maximum EQE and low-efficiency roll-off.

Aluminum doped Zinc oxide anode film for performance enhancement of trilayer fluorescence organic light emitting diode

The industrialization of fluorescence organic light-emitting diodes (OLEDs) has seriously been impacted by high fabrications cost and a short device lifespan. Particularly for transparent conductive anodes (TCA) in an OLED, which benefit manufacturing the simplest configuration with an abundant platform, more flexibility, potentially low cost-effective, and wide-ranging light flux. The goal of this effort has been to look into the possibility of aluminum-doped zinc oxide (AZO) as TCA, typically AZO/SpiroOMeTAD/Alq3: Ir(ppy)3/Bphen/LiF/Al structure is remarkably thought-out by drift–diffusion model. In addition, maximizing the light flux and minimizing the knee voltage necessitates a well-organized trilayer bandgap alignment towards exciton confinement and steadiness charge carrier transport. To enhances the hysteresis of the recombination prefactor through the higher hopping mechanism, the organic layers are staked in between AZO anode and bilayer cathode (LiF/Al) units. Moreover, optimization of the device structure is intended to eliminate the influence on OLED performances under the better thickness adjustment of consecutive layers. The maximum light flux of 1.7095 × 102 Wm−2 has been attained for 70 nm thickness of SpiroOMeTAD as hole conducting layer (HCL), 10 nm thickness of Alq3 as an organic emissive layer (OEL) with Ir(ppy)3 emitter, and 80 nm thickness of Bphen as electron conducting layer (ECL). The exposed different optoelectronic appearance curve signifies the maximum charge carrier density and current density of 1.18 × 1024 m−3, and 1.035 × 106 Am−2 for knee voltages of 2.64 V. The highest recombination prefactor of 1.174 × 10-21 m-6s−1 is achieved at 300 K for different opto-electrical considerations. Hence, future studies may be an alternative strategy for enlightening the efficiency of AZO anode-based OLEDs.

Four-Winged Propeller-Shaped Indole-Modified and Indole-Substituted Tetraphenylethylenes: Greenish-Blue Emitters with Aggregation-Induced Emission Features for Conventional Organic Light-Emitting Diodes.

Aggregation-induced emission (AIE) is an extraordinary photochemical phenomenon described by Tang's group in 2001, where the aggregation of some organic molecules enhances their light emission by limiting intramolecular activity in the aggregate state. This phenomenon offers new opportunities for researchers due to its potential applications in optoelectronics, energy, and biophysics. Tetraphenylethylenes (TPEs) are reliable AIE luminogens with a wide range of successful applications in material chemistry. To expand the library of AIE-active TPEs, both a series of TPE analogues, in which the phenyl rotor has been replaced by the indole ring, and indole-substituted TPE derivatives were designed and synthesized through vinyl-aryl and aryl-aryl bond formations using the Suzuki coupling reaction. Efficient synthetic routes that delivered indole-modified and indole-substituted TPEs have been developed, and almost all heterocyclic TPE analogues have demonstrated AIE behavior. Furthermore, to test whether the indole ring can be diversified, two title compounds were converted to a series of bis(indolyl)methane (BIM), and these BIM-TPE materials showed typical AIE properties. Interestingly, two compounds indicated a solvent vapor fuming reversible switch between bright blue emission and greenish-yellow emission. Upon fuming with dichloromethane, their fluorescence spectra showed 8 and 32 nm red-shift and could return to the original state after fuming with hexane. Furthermore, we have explored the effects of replacing the phenyl ring in TPE with indole together with the substitution of TPE with indole ring(s) on the performance of organic light-emitting diode (OLED) device applications. In addition, density functional theory calculations; the optical, electrochemical, light emission, electroluminescence characteristics; and admittance spectroscopic analysis of OLED devices of four representative TPEs have been investigated in detail. As a result, the indole-TPEs are potential blue emitters with AIE features for conventional OLEDs, which is a significant color in displays and lighting.

Application of porous materials and structures for improving optical and thermal performance of inorganic and organic light-emitting diodes: A review

Light-emitting diodes (LEDs) are considered the most promising technology for future display and lighting applications due to their high efficiency, durability, long lifespan, and eco-friendliness. Inorganic and organic LEDs (LEDs and OLEDs) are the key components in current display and lighting applications. Porous materials are a fast-developing field of study that has unraveled and expanded an extensive array of novel properties and applications. The structural and morphological parameters of the hosted semiconductor can be controlled by modifying the pore size distribution, thickness, composition of the pore walls, geometry of the pore system, and its topology. Porous hosts provide the guest semiconductor with enhanced stability and versatility in terms of processing, which favors its integration in devices. This article reviews the current progress in the applications of porous materials and structures to improve the performance of LEDs and OLEDs. The use of the porous materials to enhance the optical performance of GaN-/InGaN-/ and AlGaN-based LEDs, porous silicon LEDs, OLEDs are presented. Furthermore, the applications of porous materials for the thermal management of LEDs are discussed.

Narrowband Emissive Thermally Activated Delayed Fluorescence Materials

AbstractOrganic thermally activated delayed fluorescence (TADF) materials have attracted significant research interest in the field of organic electronics because of their inherent advantage of 100% exciton utilization capability in organic light‐emitting diodes (OLEDs) without the use of noble metals. However, despite their high internal electroluminescence quantum efficiencies approaching unity, broad emission spectra with sizable full width at half maxima (FWHM; 60–100 nm) present a critical issue that must be solved for their application in ultrahigh‐definition OLED displays. Recently, a new paradigm of TADF materials featuring the multiple resonance (MR) effect based on heteroatom‐doped polycyclic aromatic frameworks, referred to as MR‐TADF materials, has emerged and garnered considerable research interest owing to their remarkable features of efficient narrowband emissions with extremely small FWHMs (≤30 nm). Currently, MR‐TADF materials occupy a prominent position in the cutting‐edge research on organic light‐emitting materials from both chemical and physical perspectives. This review article focuses on recent progress in narrowband emissive MR‐TADF systems from the perspective of molecular design, photophysical properties, and electroluminescence performance in OLEDs. The current status and future prospects of this advanced material technology are discussed comprehensively.

Solution-processable through-space charge-transfer emitters via solubilizing groups modification

The solubility of luminescent materials is a key parameter to improve the electroluminescent performances of solution-processed organic light-emitting diodes (OLEDs). The through-space charge transfer (TSCT) materials provide an alternative to introduce the solubilizing groups (SGs) to the linker. Herein, the tert-butyl and n-hexyl groups are introduced as SGs at C7 positions of spiro structure, named C6-DMB and tBu-DMB, away from the acceptor. This has no influence on the photophysical properties of the parent TSCT molecule. Highly efficient solution-processed OLEDs were demonstrated with the maximum external quantum efficiencies of 21.0% and 21.7%, respectively. To the best of our knowledge, these are champions in the state-of-the-art solution-processed OLEDs with TSCT emitters. This work confirmed our conjecture of constructing highly efficient soluble emitters by transforming an outstanding TSCT material from thermal evaporation to solution-processed OLEDs with SGs simply integrated on the ‘bridge’ linker.

High-performance organic photovoltaic modules using eco-friendly solvents for various indoor application scenarios

•A new ternary system was processed by THF for preparing high-performance IOPVs •A record-high efficiency of 28.84% was realized for the THF-processed IOPVs •The opaque and semitransparent modules show PCEs of 22.0% and 14.8%, respectively •The application of the ternary device in various scenarios was analyzed The development of the internet-of-thing (IoT) ecosystem has an urgent demand for convenient energy sources, such as indoor organic photovoltaics (IOPVs), to power IoT devices. However, the limited medium band-gap acceptors hinder the development of IOPVs. Herein, we report a ternary system suitable for indoor applications. Introducing BTA1 into the J52-Cl:BTA3 host blend can optimize energy offsets and molecular packing of the host materials and suppress the non-radiative recombination. Consequently, the tetrahydrofuran-processed ternary devices exhibit a power conversion efficiency (PCE) of 11.22% under 1 sun and an outstanding PCE of 28.84% under a 1,000 lux LED light. Furthermore, we have constructed large-scale opaque and semitransparent modules with PCEs of 22.0% and 14.77%, respectively. Impressively, the ternary IOPV also displays a normal organic light-emitting diode performance. This work suggests that the designed ternary system possesses great potential light-emitting functions for indoor multifunctional-integrated applications. The development of the internet-of-thing (IoT) ecosystem has an urgent demand for convenient energy sources, such as indoor organic photovoltaics (IOPVs), to power IoT devices. However, the limited medium band-gap acceptors hinder the development of IOPVs. Herein, we report a ternary system suitable for indoor applications. Introducing BTA1 into the J52-Cl:BTA3 host blend can optimize energy offsets and molecular packing of the host materials and suppress the non-radiative recombination. Consequently, the tetrahydrofuran-processed ternary devices exhibit a power conversion efficiency (PCE) of 11.22% under 1 sun and an outstanding PCE of 28.84% under a 1,000 lux LED light. Furthermore, we have constructed large-scale opaque and semitransparent modules with PCEs of 22.0% and 14.77%, respectively. Impressively, the ternary IOPV also displays a normal organic light-emitting diode performance. This work suggests that the designed ternary system possesses great potential light-emitting functions for indoor multifunctional-integrated applications.

Near‐Infrared Light‐Emitting Diodes from Organic Radicals with Charge Control

AbstractOrganic radicals with fluorescence from doublet‐spin energy manifolds circumvent efficiency limits from singlet–triplet photophysics in organic light‐emitting diodes (OLEDs). The singly occupied molecular orbital (SOMO) in radicals enables the higher potential performance. The SOMO also presents substantially lower energy frontier orbitals compared to conventional fluorescent emitters for device operation, which can cause severe electron trapping that limits the performance of radical OLEDs. To improve optoelectronic performance, electron donor–acceptor‐mixed hosts are used to control charge transport for enhanced radical electroluminescence by charge recombination on SOMO and frontier orbitals. The (2‐chloro‐3‐pyridyl)bis(2,4,6‐trichlorophenyl)methyl‐based radical is designed to test the charge‐controlled device architectures in OLEDs by transient analysis and device characterization studies. Efficient radical OLEDs with 4.7% maximum external quantum efficiency are reported—showing substantial advances in performance for OLEDs with peak emission beyond 800 nm. In addition, substantially improved performance at higher current density operation and more than two orders of higher lifetime stability are achieved with mixed hosts. These results enable pathways to infrared‐emitting devices with applications ranging from communications to bioimaging.

Effects of charge mobilities and exciton blocking capabilities of charge blocking layers on the performance of organic light-emitting diodes

Blue thermally activated delayed fluorescence organic light-emitting diodes (OLEDs) have been fabricated using engineered charge blocking layers. It is found that the device efficiency increases with increasing the exciton blocking capability of electron blocking layer. But the device stability decreases concomitantly, mostly because the hole mobility of electron blocking layer decreases with exciton blocking capability increasing, thereby leading to the smaller width of exciton formation zone. In addition, the device stability decreases with the electron mobility of hole blocking layer decreasing, despite nearly same exciton blocking capabilities, mainly because the width of exciton formation zone decreases with the electron mobility of hole blocking layer decreasing. The width of exciton formation zone is understood based on the transit times for holes from anode to exciton formation zone and for electrons from cathode to exciton formation zone. We provide some in-depth insight useful for the delicate design of fluorescent, phosphorescent, and thermally activated delayed fluorescence OLEDs.

Novel Polycyclic Fused Amide Derivatives: Properties and Applications for Sky-blue Electroluminescent Devices.

Aromatic imide derivatives play a critical role in boosting the electroluminescent (EL) performance of organic light-emitting diodes (OLEDs). However, the majority of aromatic imide-based materials are limited to long wavelength emission OLEDs rather than blue emissions due to their strong electron-withdrawing characteristics. Herein, two novel polycyclic fused amide units were reported as electron acceptor to be combined with either a tetramethylcarbazole or acridine donor via a phenyl linker to generate four conventional fluorescence blue emitters of BBI-4MeCz, BBI-DMAC, BSQ-4MeCz and BSQ-DMAC for the first time. BSQ-4MeCz and BSQ-DMAC based on a BSQ unit exhibited higher thermal stability and photoluminescence quantum yields than BBI-4MeCz and BBI-DMAC based on a BBI unit due to their more planar acceptor structure. The intermolecular interactions that exist in the BSQ series materials effectively inhibit the molecular rotation and configuration relaxation, and thus allow for blue-shifted emissions. Blue OLED devices were constructed with the developed materials as emitters, and the effects of both the structure of the polycyclic fused amide acceptor and the electron donor on the EL performance were clarified. Consequently, a sky-blue OLED device based on BSQ-DMAC was created, with a high maximum external quantum efficiency of 4.94% and a maximum luminance of 7761 cd m−2.

Strategy to improve the performance of solution-processed phosphorescent organic light-emitting diodes using heteroleptic green Ir(III) complexes bearing multi-functional units

For solution-processed phosphorescence organic light-emitting diodes (PHOLEDs), two multi-functional units functionalized green triplet emitters Ir(ET)-Pic and Ir(HT)-Pic were designed and synthesized. They were synthesized by employing a 2-ethylhexyl substituted amide-bridged phenylpyridine moiety applied as main ligand and picolinate (Pic) as an ancillary ligand. In addition, the 1,3-bis(N-carbazolyl)benzene (mCP) and 1,3,4-oxadiazole (OXD) groups were introduced into 3-position of main ligand via non-conjugated benzyl ether linkage. Ir(ET)-Pic and Ir(HT)-Pic exhibited an intensive green photoluminescence (PL) emission at 502 nm, narrowed full-width at half maximum (FWHM), high PL quantum yields (PLQYs) and good solubility in organic solvents. Hence, the hole injection layer optimized device using Ir(ET)-Pic and Ir(HT)-Pic as dopants showed excellent performances with a maximum external quantum efficiency (EQEmax) of 21.5 and 19.6%, and the maximum current efficiency (CEmax) of 79.4 and 69.2 cd A−1 with Commission International L'Eclairage (CIE x,y) color coordinates of (0.36, 0.60) and (0.31,0.62), respectively. In addition, we found that the presence of bulky mCP unit in the Ir(III) complex affect the hole transport characteristics in the emissive layer. The result findings, the construction of multi-functional Ir(III) complexes are an attractive design strategy for fabrication of highly efficient green solution-processed PHOLEDs.

Investigation of improving organic light-emitting diodes efficiency using an ultra-thin ultraviolet-ozone-treated Nb-doped ZnO film as anode buffer layer

In this study, ultraviolet (UV)-ozone treated ultrathin Nb-doped ZnO (NZO) films are developed as an efficient anode buffer layer to improve the overall performance of organic light-emitting diodes (OLEDs). The results show that the UV-ozone treated NZO buffer layer containing 1 mol% of Nb2O5 possesses a higher oxygen content and a greater work function (5.22 eV) as compared to that of an indium tin oxide (ITO) film (~4.7 eV) signifying a reduction in hole injection barrier and thus an improvement in the injection efficiency. In addition, UV-ozone treatment can increase the surface energy of NZO films while reducing their surface roughness. Importantly, the UV-ozone treated 1 nm-thick NZO film with a Nb2O5 doping concentration of 1 mol% can help to lower the turn-on voltage from 3.2 V to 2.8 V, increase the luminance from 10,450 cd/m2 to 25370 cd/m2, and improve the current efficiency from 3.46 cd/A to 5.26 cd/A, (~52 % enhancement as compared to the standard OLED device). Moreover, OLEDs with the developed buffer layer reveal a significant improvement in the roll-off phenomenon under high current densities, indicating a key role of the optimized NZO film in enhancing the carrier balance of the devices. When applied to the p-i-n structure, the NZO film also lead to a superior device performance as compared to the conventional p-i-n structure using NPB:MoO3 as a hole injection layer, suggesting a widespread use of the developed thin film. These findings therefore show a promising use of the UV-ozone treated NZO ultrathin film as an effective anode buffer material for enhancing OLED overall performance.

Slow recombination of the de-trapped carriers from doped OLEDs induced by spontaneous orientation polarization

The spontaneous orientation polarization (SOP) induced by molecular permanent dipole moment has recently been discovered and plays an important role in the photoelectric performances of small molecular organic light-emitting diodes (OLEDs). However, the effect of SOP on the transient electroluminescence (TEL) dynamics of OLEDs is still vague. Herein, we find that the generation of the spike at the TEL falling edge in doped OLEDs depends remarkably on the SOP in the devices. That is, SOP is a disadvantage for spike formation and even causes the spike to disappear totally. In addition, a long-lived EL decay was observed in the OLEDs with strong SOP. Through a series of control experiments, it has been confirmed that the SOP-induced internal electric field in doped OLEDs would slow down the recombination process of the de-trapped carriers, leading to a suppression of the TEL spike and a long-lived EL decay. Accordingly, our findings not only supplement the prerequisites for the generation of the TEL spike, i.e., with weak SOP effects in an emissive layer, but also deepen the fundamental understanding of the SOP role in the TEL dynamics process of OLEDs.