Radiative Recombination Efficiency Research Articles

Grain size control in quasi-two-dimensional perovskite thin film via intermediate phase engineering for efficient bound exciton generation

AbstractQuasi-two dimensional (2D) perovskites have emerged as a promising class of materials due to their remarkable photoluminescence efficiency, which stems from their exceptionally high exciton binding energies. The spatial confinement of excitons within smaller grain sizes could enhance the formation of biexcitons leading to higher radiative recombination efficiency. However, the synthesis of high-quality quasi-2D perovskite thin films with controllable grain sizes remains a challenging task. In this study, we present a facile method for achieving quasi-2D perovskite thin films with controllable grain sizes ranging from 500 to 900 nm. This is accomplished by intermediate phase engineering during the film fabrication process. Our results demonstrate that quasi-2D perovskite films with smaller grain sizes exhibit more efficient bound exciton generation and a reduced stimulated emission threshold down to 15.89 µJ cm−2. Furthermore, femtosecond transient absorption measurements reveal that the decay time of bound excitons is shorter in quasi-2D perovskites with smaller grain sizes compared to that of those with larger grains at the same pump density, which is 230.5 ps. This observation suggests a more efficient exciton recombination process in the smaller grain size regime. Our findings would offer a promising approach for the development of efficient bound exciton lasers.

High-Voltage Stable Perovskite Light-Emitting Diodes Enabled by an Optoelectric-Tunable Sandwiched Nanostructure.

While metal halide light-emitting diodes (PeLEDs) with unique optoelectronic properties are promising emitters for next-generation displays, their performance degrades rapidly due to severe ion migration during continuous operation, especially at high voltages. Here, we realize highly stable PeLEDs by designing inorganic dielectric/perovskite semiconductor emitter/organic dielectric sandwiched nanostructures to mitigate ion migration via regulating the electric field distribution. The bilateral cesium carbonate (Cs2CO3) and tetraoctylammonium bromide (TOAB) thin interlayers can not only largely reduce the voltage imposed on the perovskite layer by serving as series resistors and, thus, mitigate the ion migration but also regulate the charge carrier transfer to improve the radiative recombination efficiency. In addition, the underneath inorganic Cs2CO3 film also provides more heterogeneous nucleation sites for growing high-crystallinity perovskite crystals, while the atop TOAB with bifunctional groups (organic amino and Br- ions) refines the morphology and enhances the optical properties of the perovskite film. As a result, efficient and stable green PeLEDs based on such an optoelectric-tunable nanostructure exhibit extremely slow efficiency decay as the applied voltage increases, and the external quantum efficiencies were maintained over 10% at a high bias up to 20 V.

MicroLEDs for optical neuromorphic computing—application potential and present challenges

Abstract The slow non-radiative surface recombination velocity of gallium nitride (GaN) in combination with its highly efficient radiative recombination makes this material ideally suited for microLEDs with dimensions as small as 1 µm and even below, serving as the fundamental building block of micro-displays. However, due to their superior miniaturization potential and energy efficiency, GaN-based microLEDs have applications that extend well beyond display technology. Their capability to produce optical patterns with high resolution, which can be modulated at extremely high frequencies, makes them suitable for numerous other applications. We suggest exploiting these exciting properties for a new and potentially equally significant application: utilizing microLEDs in optical processing units for artificial intelligence workloads. In neuromorphic computing, relevant aspects of biological neural networks are emulated directly with either electronic circuits or photonic devices, avoiding the shortcomings of conventional digital computer technology for AI workloads, which generally require massively parallel information processing. GaN microLEDs are discussed here as a promising enabling technology for optical neuromorphic processing units. We see great potential to substantially decrease power consumption through massively parallel in-memory processing combined with efficient photon production and detection. A theoretical analysis of scalability and energy efficiency is provided. A macroscopic bench-top optical microLED demonstrator is presented, which experimentally proves the feasibility of our approach. Future potential and challenges associated with miniaturizing and scaling microLED-based optical processing units are discussed. Finally, we summarize the open research questions that require attention before fully functional and miniaturized optical neuromorphic processing units based on GaN microLEDs can be realized.

Homogenizing Energy Landscape for Efficient and Spectrally Stable Blue Perovskite Light-Emitting Diodes.

Blue perovskite light-emitting diodes (PeLEDs) have attracted enormous attention; however, their unsatisfactory device efficiency and spectral stability still remain great challenges. Unfavorable low-dimensional phase distribution and defects with deeper energy levels usually cause energy disorder, substantially limiting the device's performance. Here, an additive-interface optimization strategy is reported to tackle these issues, thus realizing efficient and spectrally stable blue PeLEDs. A new type of additive-formamidinium tetrafluorosuccinate (FATFSA) is introduced into the quasi-2D mixed halide perovskite accompanied by interface engineering, which effectively impedes the formation of undesired low-dimensional phases with various bandgaps throughout the entire film, thereby boosting energy transfer process for accelerating radiative recombination; this strategy also diminishes the halide vacancies especially chloride-related defects with deep energy level, thus reducing nonradiative energy loss for efficient radiative recombination. Benefitting from homogenized energy landscape throughout the entire perovskite emitting layer, PeLEDs with spectrally-stable blue emission (478nm) and champion external quantum efficiency (EQE) of 21.9% are realized, which represents a record value among this type of PeLEDs in the pure blue region.

Ultrafast Rejuvenation of Aged CsPbI3 Quantum Dots and Efficiency Improvement by Sequential 1-Dodecanethiol Post-Treatment Strategy.

Metal halide perovskite CsPbI3 quantum dots (QDs) have sparked widespread research due to their intriguing optoelectronic. However, the CsPbI3 QDs undergo inevitable aging and luminescence quenching caused by the weak binding ability of oleate (OA-)/oleylammonium (OAm+), hindering further practical application. Herein, we have realized ultrafast rejuvenation of the aged CsPbI3 QDs that have lost their photoluminescence performance based on a 1-dodecanethiol (DDT) surface ligand to restore the outstanding red light emission with a high photoluminescence quantum yield (PLQY) from 25 to 90%. Furthermore, CsPbI3 QDs with DDT surface treatment maintain a cubic phase and high PLQY value even after 35 days. The DDT ligands can form a strong bond with Pb2+ and passivate I- ion vacancies, enhancing radiative recombination efficiency and thereby improving the PLQY of the QDs. The stable yet easily accessible surface of the DDT-capped CsPbI3 QDs was successfully employed as white LEDs and exhibited considerable enhanced luminous performance, suggesting promising application in solid-state lighting fields.

Tailoring Niox/Perovskite Interface via a Multifunctional Self‐Assembled Molecule for High‐Performance Blue Perovskite Light‐Emitting Diodes

Nickel oxide (NiOx) serves as one of the most promising hole transport materials for perovskite light‐emitting diodes (PeLEDs). However, only moderate PeLED performances have been reported on the pristine NiOx layer due to insufficient hole injection, interfacial exciton quenching, and poor perovskite quality. Herein, a multifunctional molecule of 3‐mercapto‐1‐propanesulfonate (MPS) is demonstrated to successfully tailor the NiOx–perovskite heterogenous interface by addressing the above issues. In detail, the large binding energy between mercapto sulfur and nickel induces preferential self‐assembly of the mercapto group on the NiOx surface, which simultaneously enlarges the NiOx work function by the formation of interfacial dipole and suppresses the trap‐assisted exciton quenching by the passivation of the oxygen vacancies. Meanwhile, the self‐assembled MPS on NiOx also favors high‐quality perovskite films with good morphology, high crystallinity, and reduced defects for efficient carrier radiative recombination. As a result, blue PeLEDs show a remarkable efficiency of 10.4%, representing one of the highest efficiencies for NiOx‐based blue PeLEDs, as well as a very low turn‐on voltage of 2.8 V. Consequently, this work contributes to an efficient approach to tailor the NiOx–perovskite interface for highly efficient blue PeLEDs.

Energy Level Gradients from Surface to Bulk in Hybrid Metal-Halide Perovskite Thin Films

Variations in local strain, defect densities, and composition of hybrid metal-halide perovskites have been reported to create heterogeneous energy landscapes in thin films, which impact charge-carrier diffusion and recombination dynamics. Here, we employ one- and two-photon transient absorption spectroscopy to selectively probe the dynamics of charge carriers from surface and bulk regions of methylammonium lead bromide thin films. Differences in the transient absorption spectra indicate that an energy gradient of approximately 100 meV is formed between the higher band-gap surface and lower band-gap bulk regions. Thus, during their lifetime, photoexcited carriers move away from the surface to recombine in the bulk, where our experiments detect long-lived charge populations despite the significant band splitting that has conventionally been assumed to inhibit efficient radiative recombination. Supported by first-principles calculations, we demonstrate that bright emission can still arise from the bulk with states that occupy a wide range of momenta in the vicinity of the band extrema, which show strong dipole transitions. Our results report that photoexcitations in the hybrid perovskites avoid defect-rich surface regions, and that particularly strong emission is generated from accumulated excitation populations in the bulk. Published by the American Physical Society 2024

InGaAs/AlGaAs MQWs grown by MBE: Optimizing GaAs insertion layer thickness to enhance interface quality and luminescent property

The refinement of interface structure in InGaAs/AlGaAs multiple quantum wells (MQWs) through molecular beam epitaxy (MBE) is crucial for enhancing their luminescence performance. The influencing mechanisms of the GaAs insertion layer (ISL) thicknesses on the interface structure and luminescence properties of InGaAs/AlGaAs MQWs were investigated by varying the GaAs ISL thickness variations and optimizing growth parameters. In our designed InGaAs/AlGaAs MQWs structures, GaAs ISL with thickness variables of 0 nm, 0.5 nm, 1 nm, 2 nm, and 4 nm were inserted between the interfaces of the InGaAs well layer and the AlGaAs barrier layer. Through experimental characterizations. The introduction of the GaAs ISL resulted in a gradual transition of the MQWs surface morphology from a three-dimensional (3D) island structure to a typical step-flow surface morphology, leading to the reduction in surface roughness and enhancement of hetero-interfaces quality. Moreover, the GaAs ISL with thickness exceeding 2 nm effectively inhibited the segregation of indium atoms, promoting the ordering of interface alloys and decreasing the polarization degrees from 3.76 % to 2.09 %. Temperature-dependent PL measurements indicated that the GaAs ISL could reduce interface defects and the density of non-radiative recombination centers, thereby enhancing the radiative recombination efficiency of MQWs and ultimately increasing the peak intensity of photoluminescence by 3.4 times. This work is significance for understanding the luminescent properties of InGaAs/AlGaAs MQWs, which provides reference highly efficient optoelectronic devices development.

Efficient Large-Area (81 cm2) Ternary Copper Halides Light-Emitting Diodes with External Quantum Efficiency Exceeding 13% via Host-Guest Strategy.

Ternary copper (Cu) halides are promising candidates for replacing toxic lead halides in the field of perovskite light-emitting diodes (LEDs) toward practical applications. However, the electroluminescent performance of Cu halide-based LEDs remains a great challenge due to the presence of serious nonradiative recombination and inefficient charge transport in Cu halide emitters. Here, the rational design of host-guest [dppb]2Cu2I2 (dppb denotes 1,2-bis[diphenylphosphino]benzene) emitters and its utility in fabricating efficient Cu halide-based green LEDs that show a high external quantum efficiency (EQE) of 13.39% are reported. The host-guest [dppb]2Cu2I2 emitters with mCP (1,3-bis(N-carbazolyl)benzene) host demonstrate a significant improvement of carrier radiative recombination efficiency, with the photoluminescence quantum yield increased by nearly ten times, which is rooted in the efficient energy transfer and type-I energy level alignment between [dppb]2Cu2I2 and mCP. Moreover, the charge-transporting mCP host can raise the carrier mobility of [dppb]2Cu2I2 films, thereby enhancing the charge transport and recombination. More importantly, this strategy enables a large-area prototype LED with a record-breaking area up to 81 cm2, along with a decent EQE of 10.02% and uniform luminance. It is believed these results represent an encouraging stepping stone to bring Cu halide-based LEDs from the laboratory toward commercial lighting and display panels.

Suppressing nonradiative recombination enables highly efficient red perovskite light-emitting diodes

Quasi-two-dimensional perovskites are promising emitters for red light-emitting diodes. However, the practical application of red perovskite light-emitting diodes (PeLEDs) is still limited by the defect-induced nonradiative recombination. In this study, we demonstrate efficient red PeLEDs by introducing the diethylene glycol bis(3-aminopropyl) ether (DGBE) additive. The coupling effect between oxygen (O) atoms in DGBE and unsaturated Pb2+ not only regulates crystallization, but also passivates defects. Benefiting from the reduced defect densities and enhanced radiative recombination efficiencies, the photoluminescence quantum yield (PLQY) increases from 39 % to 80 %. Consequently, we achieve high-performance red PeLEDs with a maximum external quantum efficiency of 24.2 %, which provides a reliable approach to promote the development of highly efficient red PeLEDs.

Radiative and Nonradiative Recombination Processes in AlGaN Quantum Wells on Epitaxially Laterally Overgrown AlN/Sapphire from 10 to 500 K

Radiative and nonradiative recombination processes are investigated in the temperature range from 10 to 500 K for AlGaN quantum wells on epitaxially laterally overgrown AlN/sapphire templates. Time‐integrated photoluminescence (PL) spectroscopy under selective excitation conditions demonstrates that the decrease in the radiative recombination efficiency with increasing temperature is one of the causes of the thermal droop in AlGaN‐based deep‐ultraviolet (DUV) light‐emitting diodes. Time‐resolved PL spectroscopy indicates that not only the decreasing nonradiative recombination lifetime but increasing radiative recombination lifetime with increasing temperature contributes to the thermal droop. The temperature dependence of the radiative recombination lifetime is discussed, revealing that luminescence linewidth is a valuable criterion for designing efficient AlGaN‐based DUV emitters.

Non-heavy doped pnp-AlGaN tunnel junction for an efficient deep-ultraviolet light emitting diode with low conduction voltage.

While traditional tunnel junction (TJ) light-emitting diodes (LEDs) can enhance current diffusion and increase hole injection efficiency, their reliance on highly doped AlGaN layers to improve hole tunneling efficiency results in a higher conduction voltage, adversely impacting LED device performance. This paper proposes a non-heavy doped pnp-AlGaN TJ deep ultraviolet (DUV) LED with a low conduction voltage. By inserting the TJ near the active region, between the electron blocking layer and the hole supply layer, the need for heavily doped AlGaN is circumvented. Furthermore, the LED leverages the polarization charge in the pnp-AlGaN TJ layer to decrease the electric field strength, enhancing hole tunneling effects and reducing conduction voltage. The non-heavy doped pnp-AlGaN TJ LED effectively enhances carrier concentration in the quantum well, achieving a more uniform distribution of electrons and holes, thus improving radiative recombination efficiency. Consequently, at an injection current of 120 A/cm2, compared to the traditional structure LED (without TJ), the proposed LED exhibits a 190.7% increase in optical power, a 142.8% increase in maximum internal quantum efficiency (IQE) to 0.85, and a modest efficiency droop of only 5.8%, with a conduction voltage of just 4.1V. These findings offer valuable insights to address the challenges of high heavy doped TJ and elevated conduction voltage in high-performance TJ DUV LEDs.

Dramatically Enhanced Light‐Emitting/Detecting Bifunction of CH3NH3PbBr3 Single‐Crystal Thin‐Film via Electrical Doping‐Induced Defects Passivation

AbstractHigh‐performance light‐emitting/detecting bifunctional optoelectronic devices based on halide perovskites are hindered by the less efficient carrier transport and radiative recombination processes. The density of defects (i.e., surface and bulk defects) is the main factor affecting carrier transport, radiation recombination, and determining performance in perovskites. Therefore, techniques to effectively regulate defects are highly needed. Here, a convenient and effective strategy, electrical doping, is proposed to flexibly regulate defect density, resulting in dramatically enhanced light‐emitting (i.e., fluorescence and carrier lifetime) and light‐detecting performance (i.e., hole mobility, photo‐responsivity, and photo‐detectivity) simultaneously. An improved carrier transport model in CH3NH3PbBr3 (MPB) single‐crystal thin‐film (SCTF) is proposed to elucidate the regulation mechanism of defects and carrier transport under electrical doping. These results show that the surface defect density can be effectively reduced by 47.49% under optimal electrical poling intensity (0.168 V µm−1), and photoluminescence intensity and carrier lifetime can be increased by 259% and 89.98%, respectively. Furthermore, planar MPB SCTF photodetector exhibits hole mobility increased by 14.97%, photo‐responsivity increased by 82.78%, and photo‐detectivity increased by 868% at 0.168 V µm−1. Particularly, a record photo‐detectivity of 3.53 × 1013 Jones is achieved under electrical doping. This study provides guidance for flexibly adjusting defect density and optimizing perovskite SCTFs light‐emitting/detecting bifunctional devices.

Harnessing Conformational Disorder of Organic Cations for Efficient Blue Quasi‐2D Perovskite LEDs

AbstractDespite quasi‐2D perovskite offering great control over the optoelectronic properties, disordered organic cations are often perceived as detrimental to device performance, primarily affecting charge carrier mobility. However, it is proposed that such disordered organic cations‐enabled excellent excitonic properties can be beneficial for fabricating high‐efficiency perovskite light‐emitting diodes (PeLEDs) facilitated by reduced dielectric screening effect. Here, by incorporating acetamidinium bromide additives, the conformational disorder of organic cation is precisely manipulated and meticulously probed using sum frequency generation vibrational spectroscopy. Finally, a distinctive inverse relationship is elucidated between the degree of conformational order, characterized as relative structure ordering , and key performance metrics such as photoluminescence quantum yield and external quantum efficiency (EQE). By optimizing the configurational disorder, sky‐blue (485 nm) PeLEDs achieve a noteworthy EQE of 14.42% and exhibit significantly prolonged operational stability in open‐air conditions. This finding underscores the potential advantages of disordered organic cations in enhancing exciton properties and radiative recombination efficiency.

Influence of period number of superlattice electron barrier layer on the performance of AlGaN-based deep ultraviolet LED

The development of AlGaN-based deep ultraviolet light emitting diodes (DUV-LEDs) is currently limited by poor external quantum efficiency (EQE) and wall-plug efficiency (WPE). Internal quantum efficiency (IQE), as an important component of EQE, plays a crucial role in improving the performance of DUV-LEDs. The IQE is related to the carrier injection efficiency and the radiation recombination rate in the active region. In order to improve the IQE of AlGaN-based DUV-LEDs, this work proposes a scheme to optimize the period number of superlattice electron barrier layer (SL-EBL) to achieve better carrier injection efficiency and confinement capability. The effect of the period number of SL-EBL on the luminous efficiency, reliability and carrier recombination mechanism of AlGaN-based DUV-LEDs with an emission wavelength of 273 nm are investigated. The experimental results show that the light output power (LOP), external quantum efficiency (EQE) and wall-plug efficiency (WPE) of the DUV-LEDs tend to first increase and then decrease with the period number of SL-EBL increasing, while the leakage current decreases and the reliability is enhanced. The maximum EQE and WPE of the DUV-LED are 3.5% and 3.2%, respectively, at an injection current of 7.5 mA when the period number of SL-EBL is fixed at 7 (the thickness is 28 nm). Meanwhile, the numerical simulation results show that the electron potential barrier height is enhanced with the period number of SL-EBL increasing, and the variation of the hole potential barrier height is negligible. Therefore, increasing the period number of SL-EBL is beneficial to shielding the dislocations and suppressing the leakage of electrons into the p-type layer, which improves the luminous efficiency and reliability of DUV-LEDs. However, when the period number of SL-EBL exceeds 7, the excessively thick hole potential barrier prevents the holes from entering into the activation region and reduces the radiative recombination efficiency. Therefore, EQE and WPE will show an inflection point with the variation of the period number of SL-EBL. In addition, to investigate the carrier recombination mechanism of the active region, the experimental EQE curves are fitted by the ABC model as well as the different slopes in logarithmic light output power-current (<i>L-I</i> ) curves are calculated after aging. It can be found that increasing the period number of SL-EBL can effectively suppress the non-radiative combination of carriers in the active region. This investigation can provide an alternative way to enhance the photoelectric performance of DUV-LEDs.

Efficient Perovskite Light‐Emitting Diodes Enabled by Nickel Acetate Interlayer

AbstractMetal halide perovskite light‐emitting diodes (Pero‐LEDs) have gained great attention due to their promising applications in lighting and displays. However, in their conventional three‐layered sandwich structure, some undeserved carrier behaviors, such as imbalanced carrier injection, severe carrier loss, and unstable recombination zone, limit the device's performance. Herein, a four‐layered design by inserting a nickel acetate (Ni(OAc)2) interlayer between the emitter and hole‐transport layer(HTL) to manage carrier behavior and improve radiative recombination efficiency is proposed. Specifically, the Ni(OAc)2 interlayer is poorly conductive and can partially block the hole injection, making the hole‐electron injection more balanced. And the Ni(OAc)2 interlayer avoids the direct contact between the perovskite emitter and hole transporter, reducing the interfacial carrier quenching. Moreover, the Ni(OAc)2 interlayer inhibits the electron‐migrated recombination at the hole transporter interface, confining the carrier recombination zone in the emitter layer. As a result, the corresponding Pero‐LEDs achieve a maximum external quantum efficiency (EQEmax) of 24.6% with good reproducibility, showing an average EQEmax of over 20%.

Highly Bright and Stable Lead-Free Double Perovskite White Light-Emitting Diodes.

Lead-free double perovskites (DPs) are emerging highly stable emitters with efficient broadband self-trapped exciton (STE) photoluminescence (PL), but their low electroluminescent (EL) efficiency is a critical shortcoming. This work promotes the external quantum efficiency (EQE) and luminance of DP-based white light-emitting diode (wLED) with a normal device structure to 0.76% and 2793cd m-2 via two modifications: This work prevents the formation of adverse metallic silver, spatially confined STE, and lowers local site symmetry in Cs2 Na0.4 Ag0.6 In0.97 Bi0.03 Cl6 DP by terbium doping; and this work develops a guest-host strategy to improve film morphology, reduce defect density, and increase carrier mobility. These alterations cause substantial increase in STE radiative recombination and charge injection efficiency of perovskite layer. Finally, pure white EL with ideal color coordinates of (0.328, 0.329) and a record-breaking optoelectronic performance is achieved by introducing additional green carbon dots in LED to fill the deficient green component.

Scalable Bilayer MoS2‐Based Vertically Inverted p–i–n Light‐Emitting Diodes

AbstractHerein, a vertically inverted p–i–n architecture of light‐emitting diodes (LEDs) is designed for manufacturing feasibility and demonstrated scalable bilayer MoS2‐based LEDs. A 4 inch scale bilayer MoS2 is prepared by a two‐step growth method allocating the pre‐deposition of a few‐nm thick metal film and post‐sulfurization. To apply bilayer MoS2 for an active layer in LEDs, the film is transferred over ZnO nanoparticle layers, an electron transfer layer, and then the rest of the LED components are constructed by thermal deposition. This vertically inverted LED architecture allows individual organic or inorganic components to incorporate without degradation during the wet‐transfer process and transfer electron or hole carriers across separate layers, resulting in efficient radiative recombination in the MoS2 emitting layer. MoS2‐based LEDs exhibit electroluminescence of ≈5.41 cd m−2 throughout four active areas of 6.25 mm2 at a driving voltage of 7 V. Therefore, this achievement can overcome the drawbacks of existing transition metal dichalcogenides (TMDs)‐based optoelectrical applications and extend its potential in various fields, such as flexible, ultrathin, or transparent displays.

Porous pseudo-substrates for InGaN quantum well growth: Morphology, structure, and strain relaxation

Strain-related piezoelectric polarization is detrimental to the radiative recombination efficiency for InGaN-based long wavelength micro-LEDs. In this paper, partial strain relaxation of InGaN multiple quantum wells (MQWs) on the wafer scale has been demonstrated by adopting a partially relaxed InGaN superlattice (SL) as the pseudo-substrate. Such a pseudo-substrate was obtained through an electro-chemical etching method, in which a sub-surface InGaN/InGaN superlattice was etched via threading dislocations acting as etching channels. The degree of strain relaxation in MQWs was studied by x-ray reciprocal space mapping, which shows an increase of the in-plane lattice constant with the increase of etching voltage used in fabricating the pseudo-substrate. The reduced strain in the InGaN SL pseudo-substrate was demonstrated to be transferable to InGaN MQWs grown on top of it, and the engineering of the degree of strain relaxation via porosification was achieved. The highest relaxation degree of 44.7% was achieved in the sample with the porous InGaN SL template etched under the highest etching voltage. Morphological and structural properties of partially relaxed InGaN MQWs samples were investigated with the combination of atomic force and transmission electron microscopy. The increased porosity of the InGaN SL template and the newly formed small V-pits during QW growth are suggested as possible origins for the increased strain relaxation of InGaN MQWs.

Dual-functionalized poly(ethylene oxide) for interface modification and addition of rubidium-doped CsPbBr3 perovskite composite emission layer to enhance brightness of perovskite light-emitting diodes

Metal halide perovskite as an emitter has extremely high color purity, but the generally poor morphology of the perovskite layer restricts the performance of the emitter. The additive of a suitable polymer can greatly boost the uniformity of the spin-coated perovskite film. The all-inorganic perovskite layer deposited by the solution method has a multi-crystalline structure. Besides, there are a lot of defects and grain boundaries on the surface, and the carriers will undergo non-radiative recombination at these defects. In this study, Cs1-xRbxPbBr3 was prepared by introducing Rb+ cations with smaller ionic radius to partially replace Cs+ cations, and combined with poly(ethylene oxide) (PEO) and (1,3,5-benzinetriyl)tris(1-phenyl-1-H-benzimidazole) (TPBi) blended composite film as the light-emitting layer, that can increase the film coverage and radiative recombination efficiency of the perovskite film. The polymer PEO was introduced as a buffer layer deposited on the poly-TPD hole transport layer (HTL) to to enhance the hydrophilicity and passivate the poly-TPD HTL/perovskites interface in order to obtain high-efficiency perovskite light-emitting diodes. By adjusting the concentration of the PEO buffer layer, the champion luminance and external quantum efficiency are 25650 cd/m2 and 0.844 %, respectively.