Peak External Quantum Efficiency Research Articles

In-situ composition development of Zn/In-doped Ga2O3 nanowire with ultrahigh responsivity and long-term stability for deep-UV photodetector

High-performance deep ultraviolet photodetectors (UV PDs) based on Ga2O3 have been applied widely in civil and military exploration. The incident photon-to-electron conversion efficiency of Ga2O3-based UV PDs could be improved by doping metal or non-metal elements in the lattice. Herein, multi-metallic oxide of InZn co-doped Ga2O3 (InZn-Ga2O3) nanowires is synthesized via the in-situ chemical vapor deposition (CVD) method. The favorable 25%InZn-Ga2O3 exhibits a maximum responsivity of 440.42 A W−1 and a peak external quantum efficiency (EQE) of 2.15 × 105% under 254 nm light illumination at 10 V, which are 1.19 × 104 times higher than that for pure Ga2O3, indicating its enhanced detection ability for deep-UV light and high conversion efficiency from photons to electrons. A high UV/visible rejection ratio of 7.3 × 105 is also obtained, implying a high sensitivity for UV light. Moreover, the responsivity of the InZn-Ga2O3 UV PD remains unchanged after a long period of 8000 s testing. The superior performances of InZn-Ga2O3 UV PD are attributed to the improved crystal quality with decreased oxygen vacancies and elevated conductivity, which facilitate the separation and transfer of photoinduced electron-hole carriers. The DFT calculation and UV–vis spectra results reveal that the InZn-Ga2O3 possesses a narrowed band gap with enhanced light absorption and a decreased work function for the fast escape of electrons. In addition, the ohmic contact between InZn-Ga2O3 and Ag electrode accelerates the transfer and diffusion of photogenerated electrons. The achievements in our work present a multi-metallic oxide nanowire with high performance and an innovative mechanism analysis method for the applications of optoelectronic devices.

ZnO/silica quasi core/shell nanoparticles as electron transport materials for high-performance quantum-dot light-emitting diodes

Quantum dot light-emitting diodes (QLEDs) are considered as the ideal candidate for next-generation displays, solid-state lighting, and optical communication applications. Although the efficiency of QLEDs has been significantly improved to the level comparable to that of organic light-emitting diodes in recent years, simultaneously achieving high efficiency and high brightness still remains challenging for QLEDs. In this work, we report a facile and effective electron-transport-layer interface control strategy of incorporating 3-aminopropyl triethoxysilane (APTES) into a ZnO nanocrystal-solution to enhance charge injection balance and suppress interfacial exciton quenching via in-situ formation of ZnO/organic silica (hereinafter referred to as ZnO/SiO2) quasi core/shell nanoparticles in the solution, enabling red QLEDs to exhibit a maximum luminance intensity of 261,700 cd m−2, a peak external quantum efficiency (EQE) of 19.0%, and low efficiency roll-off at high luminance (an EQE up to 16.8% remained at a brightness of 200, 000 cd m−2). Our results demonstrate that substituting quasi core/shell-structured ZnO/SiO2 nanoparticles for traditional ZnO nanocrystals as electron transport materials is a simple and effective means of fabricating QLEDs with both high efficiency and high luminance, which is expected to facilitate the development of QLED technology toward practical applications in lighting, displays and optical communication.

Efficient Red-Emissive Circularly Polarized Electroluminescence Enabled by Quasi-2D Perovskite with Chiral Spacer Cation.

Perovskites are promising environmentally sustainable materials for circularly polarized electroluminescence (CPEL). While another chiral nonemissive layer is required for the developed perovskite-based CPEL, we report herein a highly efficient circularly polarized electroluminescence based on a single layer of quasi-2D perovskite with achiral phenethylammonium iodide (PEAI) and chiral S/R-1-(1-naphthyl)ethylammonium iodide (S/R-NEAI) as dual spacer cations. The quasi-2D perovskite was further passivated by carbazole-functionalized phosphonium. The as-fabricated film exhibits not only a circular dichroism (CD) signal but also prominent circularly polarized luminescence (CPL) activity with a maximum photoluminescence dissymmetry factor (glum) of ∼2.1 × 10-3. More importantly, a highly efficient, spin-polarized light-emitting diode (LED) was fabricated based on the in situ passivated quasi-2D perovskite with a peak external quantum efficiency of 3.7% and a maximum electroluminescence dissymmetry factor (gEL) of ∼4.0 × 10-3.

Low-efficiency-droop c-plane InGaN/GaN light-emitting diodes through the use of thick single quantum wells and doped barriers

Efficiency droop at high current densities is a problem for InGaN-based light-emitting diodes (LEDs), especially for conventional c-plane devices. The large internal electric fields in c-plane quantum wells (QWs) lead to an increase in the active region carrier density (n), causing the electrical efficiency droop onset to occur at low current densities. Here, we present an approach to reduce the internal electric fields (Eint) in c-plane QWs by placing doped p-type and n-type GaN barriers close to the QW. The reduced Eint also allows a thick QW active region design, which helps to lower n to further reduce the droop. The concept of using doped barriers to control Eint is explained using theory and device simulations. Following that, multiple series of thick single QW (SQW) LEDs were grown and characterized. Key parameters in the epitaxial design such as the doping levels and the relative position of the doped barriers were systematically studied and optimized. By using optimized doped barriers and a thick SQW, c-plane LEDs with a low-efficiency droop of 14% at 300 A/cm2 [with respect to the peak external quantum efficiency (EQE)] and a high peak EQE of 49% were demonstrated.

D-O-A based organic phosphors for both aggregation-induced electrophosphorescence and host-free sensitization

Pure organic phosphors capable of room-temperature phosphorescence show a great potential in organic light-emitting diodes, while it is limited by the big challenge to realize efficient electroluminescence under electric excitation. Herein, we develop a class of organic phosphors based on acridine as the electron donor, triazine as the electron acceptor and oxygen as the bridge between them. Benefitting from the characteristic donor-oxygen-acceptor geometry, these compounds are found to behave an exciting aggregation-induced organic room-temperature electrophosphorescence, and achieve a record-high external quantum efficiency of 15.8% for non-doped devices. Furthermore, they can sensitize multi-resonant emitters in the absence of any additional wide bandgap host, leading to an effective narrowband emission with a peak external quantum efficiency of 26.4% and a small full-width at half maximum of 26 nm. The results clearly indicate that donor-oxygen-acceptor geometry is a promising strategy to design organic phosphors suitable for organic light-emitting diodes.

Ionic Liquid Passivation for High‐Performance Sky‐Blue Quasi‐2D Perovskite Light‐Emitting Diodes

AbstractGreat progress has been made in high‐performance perovskite light‐emitting diodes (PeLEDs). However, the external quantum efficiency (EQE) of blue PeLEDs still lags. Particularly, defects are inevitable in solution‐processed perovskite films, which inhibit the efficient radiative recombination in blue PeLEDs. Herein, a facile ionic liquid (IL, 1,3‐dimethyl‐3‐imidazolium hexafluorophosphate) post‐treatment on the as‐fabricated quasi‐2D perovskite film is reported, to passivate the uncoordinated Pb through the strong interaction with IL. The IL‐assisted perovskite film demonstrates a great enhancement of radiative recombination efficiency, and the photoluminescence quantum yield of the film increases from 35.7% to 74.6%. IL post‐treatment also adjusts the energy level of perovskite film and enhances the hole injection in PeLED. As a result, the peak EQE of the sky‐blue quasi‐2D PeLED is improved from 4.0% to 9.0%, while the turn‐on voltage is reduced from 3.3 to 3.0 V. This work contributes to a feasible and effective approach for improving the quality of blue quasi‐2D perovskites and enhancing the efficiency of blue PeLEDs.

Impact of Sidewall Conditions on Internal Quantum Efficiency and Light Extraction Efficiency of Micro‐LEDs

AbstractThe sidewall condition is a key factor determining the performance of micro‐light emitting diodes (µLEDs). In this study, equilateral triangular III‐nitride blue µLEDs are prepared with exclusively m‐plane sidewall surfaces to confirm the impact of sidewall conditions. It is found that inductively coupled plasma‐reactive ion etching (ICP‐RIE) causes surface damages to the sidewall and results in rough surface morphology. As confirmed by time‐resolved photoluminescence (TRPL) and X‐ray photoemission spectroscopy (XPS), tetramethylammonium hydroxide (TMAH) eliminates the etching damage and flattens the sidewall surface. After ICP‐RIE, 100 µm2‐µLEDs yield higher external quantum efficiency (EQE) than 400 µm2‐µLEDs. However, after TMAH treatment, the peak EQE of 400 µm2‐µLEDs increases by ≈10% in the low current regime, whereas that of 100 µm2‐µLEDs slightly decreases by ≈3%. The EQE of the 100 µm2‐µLEDs decreases after TMAH treatment although the internal quantum efficiency (IQE) increases. Further, the IQE of the 100 µm2‐µLEDs before and after TMAH treatment is insignificant at temperatures below 150 K, above which it becomes considerable. Based on PL, XPS, scanning transmission electron microscopy, and scanning electron microscopy results, mechanisms for the size dependence of the EQE of µLEDs are explained in terms of non‐radiative recombination rate and light extraction.

The Synergy of the Buried Interface Surface Energy and Temperature for Thermal Evaporated Perovskite Light-Emitting Diodes.

Multisource coevaporation is such a promising method for the preparation of perovskite films. However, there is limited research about the effects of the buried interface on thermal-evaporated perovskite light-emitting diodes (PeLEDs). In this study, the effects of buried interfaces on thermal-evaporated all-inorganic perovskite films are systematically investigated. It is found that the low-surface-energy buried interface promotes the formation of columnar grain by suppressing heterogeneous nucleation, and functional groups on the high-surface-energy interface have a significant effect on the actual element ratio of the film. The substrate temperature can affect the nucleation and film-formation kinetics of the columnar grains. As a result of the synergistic strategy, a peak external quantum efficiency (EQE) of 8.6% is achieved in the green PeLEDs with a stable emission peak at 516 nm, which is among the best thermal-evaporated PeLEDs reported. This work provides an insight into the preparation of perovskites by thermal evaporation and builds the groundwork for future studies.

In-Situ Interfacial Reaction Induced Amino-Rich Oxide Surface to Grow High-Quality FAPbBr3 Crystals for Efficient Inverted Light-Emitting Diodes

Iodine-based perovskite light-emitting diodes (PeLEDs) utilizing zinc oxide (ZnO) films as electron-transporting layers (ETLs) show excellent efficiency and stability. However, the poor understanding of the reaction between bromine-based perovskites and ZnO films hinders the preparation of high-quality bromine-based perovskites on ZnO films. Here, we demonstrate an in situ interfacial amidation reaction between one amino group of formamidinium bromide (FABr) and sol–gel ZnO film, leaving unreacted amino groups to form an amino-rich ZnO/perovskite interface. The density of amino groups, which can regulate the crystallization of FAPbBr3, is determined by the original carboxylate groups of the ZnO film. Carboxylate groups-rich zinc–magnesium oxide film is further developed to grow high-quality FAPbBr3 crystals. The resultant inverted PeLEDs show a low turn-on voltage of 1.8 V and a peak external quantum efficiency of 12.7%, the highest efficiency reported for green-emissive PeLEDs prepared directly on ZnO-based films. This significant discovery provides a promising route toward achieving high-performance inverted bromine-based PeLEDs on oxide ETLs.

Bright and stable perovskite light-emitting diodes in the near-infrared range.

Perovskite light-emitting diodes (LEDs) have attracted broad attention due to their rapidly increasing external quantum efficiencies (EQEs)1-15. However, most high EQEs of perovskite LEDs are reported at low current densities (<1 mA cm-2) and low brightness. Decrease in efficiency and rapid degradation at high brightness inhibit their practical applications. Here, we demonstrate perovskite LEDs with exceptional performance at high brightness, achieved by the introduction of a multifunctional molecule that simultaneously removes non-radiative regions in the perovskite films and suppresses luminescence quenching of perovskites at the interface with charge-transport layers. The resulting LEDs emit near-infrared light at 800 nm, show a peak EQE of 23.8% at 33 mA cm-2 and retain EQEs more than 10% at high current densities of up to 1,000 mA cm-2. In pulsed operation, they retain EQE of 16% at an ultrahigh current density of 4,000 mA cm-2, along with a high radiance of more than 3,200 W s-1 m-2. Notably, an operational half-lifetime of 32 h at an initial radiance of 107 W s-1 m-2 has been achieved, representing the best stability for perovskite LEDs having EQEs exceeding 20% at high brightness levels. The demonstration of efficient and stable perovskite LEDs at high brightness is an important step towards commercialization and opens up new opportunities beyond conventional LED technologies, such as perovskite electrically pumped lasers.

Biphenyl Au(III) Complexes with Phosphine Ancillary Ligands: Synthesis, Optical Properties, and Electroluminescence in Light-Emitting Electrochemical Cells.

A series of ten cationic complexes of the general formula [(C^C)Au(P^P)]X, where C^C = 4,4'-di-tert-butyl-1,1'-biphenyl, P^P is a diphosphine ligand, and X is a noncoordinating counteranion, have been synthesized and fully characterized by means of chemical and X-ray structural methods. All the complexes display a remarkable switch-on of the emission properties when going from a fluid solution to a solid state. In the latter, long-lived emission with lifetime τ = 1.8-83.0 μs and maximum in the green-yellow region is achieved with moderate to high photoluminescence quantum yield (PLQY). This emission is ascribed to an excited state with a mainly triplet ligand-centered (3LC) nature. This effect strongly indicates that rigidification of the environment helps to suppress nonradiative decay, which is mainly attributed to the large molecular distortion in the excited state, as supported by density functional theory (DFT) and time-dependent DFT (TD-DFT) computation. In addition, quenching intermolecular interactions of the emitter are avoided thanks to the steric hindrance of the substituents. Emissive properties are therefore restored efficiently. The influence of both diphosphine and anion has been investigated and rationalized as well. Using two complexes as examples and owing to their enhanced optical properties in the solid state, the first proof-of-concept of the use of gold(III) complexes as electroactive materials for the fabrication of light-emitting electrochemical cell (LEC) devices is herein demonstrated. The LECs achieve peak external quantum efficiency, current efficiency, and power efficiency up to ca. 1%, 2.6 cd A-1, and 1.1 lm W-1 for complex 1PF6 and 0.9%, 2.5 cd A-1, and 0.7 lm W-1 for complex 3, showing the potential use of these novel emitters as electroactive compounds in LEC devices.

In-situ growth of low-dimensional perovskite-based insular nanocrystals for highly efficient light emitting diodes

Regulation of perovskite growth plays a critical role in the development of high-performance optoelectronic devices. However, judicious control of the grain growth for perovskite light emitting diodes is elusive due to its multiple requirements in terms of morphology, composition, and defect. Herein, we demonstrate a supramolecular dynamic coordination strategy to regulate perovskite crystallization. The combined use of crown ether and sodium trifluoroacetate can coordinate with A site and B site cations in ABX3 perovskite, respectively. The formation of supramolecular structure retard perovskite nucleation, while the transformation of supramolecular intermediate structure enables the release of components for slow perovskite growth. This judicious control enables a segmented growth, inducing the growth of insular nanocrystal consist of low-dimensional structure. Light emitting diode based on this perovskite film eventually brings a peak external quantum efficiency up to 23.9%, ranking among the highest efficiency achieved. The homogeneous nano-island structure also enables high-efficiency large area (1 cm2) device up to 21.6%, and a record high value of 13.6% for highly semi-transparent ones.

One-Pot Synthesis of InP Multishell Quantum Dots for Narrow-Bandwidth Light-Emitting Devices

With tunable emission in the full visible region, the ecofriendly InP quantum dots (QDs) show unique application prospects in light-emitting devices. At present, InP QDs suffer from wide-bandwidth emission, especially for electroluminescence (EL), which hinders their applications in high-performance display devices. Here, we report a facile one-pot synthesis of narrow-bandwidth InP/ZnSeS/ZnS QDs using a safe phosphorus source of tris(dimethylamino)phosphine, in which the ZnSeS inner-shell layer is formed via temperature-gradient solution growth from 240 to 280 °C. The synthesized green QDs have a high photoluminescence quantum yield (PLQY) of 91% and full width at half-maximum (fwhm) of 36 nm. Moreover, the resultant quantum dot light-emitting devices (QLEDs) also show a narrow fwhm of 42 nm, which is the narrowest emission of green InP QLEDs based on a safe phosphorus source reported so far. Further modulation of the electron injection into the device by inserting a thin layer of lithium fluoride results in a peak external quantum efficiency of 5.56%.

An efficient green-emitting quantum dot with near-unity quantum yield and suppressed Auger recombination for high-performance light-emitting diodes

Near 100% photoluminescence quantum yield (PL QY) is the first target for designing luminescent quantum dots (QDs). Here, an alloyed QD with a core/shell structure of Cd0.194Zn0.806Se0.406S0.594/ZnS is synthesized and characterized by the feature of large core size (about 10 nm) and thin shell (around three ZnS monolayers). It exhibits an efficient green emission with the PL QY of 99.8% and ultra-fast radiative transition rate (kr) of 4.16 × 107 s−1. It demonstrates that the excited state will be rapidly decayed to its ground state through a radiative channel and less vulnerable to non-radiative processes. Under a high pump intensity (254.65 μJ cm−2), the Cd0.194Zn0.806Se0.406S0.594/ZnS QD still owns a long biexciton decay lifetime (τxx) of 1.05 ns and high biexciton QYxx of 25.1%, corresponding to a suppressed non-radiative Auger recombination. The Cd0.194Zn0.806Se0.406S0.594/ZnS QD based light-emitting diode exhibits a peak external quantum efficiency of 20.1% and brightness of over 105 cd m−2 at 5.2 V. We believe that the Cd0.194Zn0.806Se0.406S0.594/ZnS QD not only provides a near-unity QY but also ensures its QD based light-emitting diode (QLED) with an excellent performance, which could be an excellent QD material for QLED applications.

High Efficiency Near-Infrared Perovskite Light Emitting Diodes With Reduced Rolling-Off by Surface Post-Treatment.

The rolling-off phenomenon of device efficiency at high current density caused by quenching of luminescence in perovskite light-emitting diodes (PeLED) is challenging to be solved. Here, 2-amino-5-iodopyrazine (AIPZ) is dissolved in a mixed solvent of chlorobenzene (CB)/isopropanol (IPA) (7:3 volume ratio) for surface post-treatment of FAPbI3 perovskite film. The interaction of AIPZ and perovskite surface not only balances the charge injection but also passivates defects to enhance radiative recombination in PeLED. Therefore, the PeLED champion yields peak external quantum efficiency reaching 23.2% at the current density of 45mA cm-2 with a radiance brightness of 290W sr-1 m-2 . More importantly, the rolling-off of device efficiency is significantly reduced. The lowest rolling-off devices can maintain 80% of peak EQE (22.1%) at a high current density of 460mA cm-2 , whereas the control device only retains 25% of the peak EQE value. This work provides an effective strategy to improve performance and reduce the EQE rolling-off of PeLED for practical application.

Hybrid tunnel junction enabled independent junction control of cascaded InGaN blue/green micro-light-emitting diodes.

We demonstrate vertical integration of nitride-based blue/green micro-light-emitting diodes (µLEDs) stacks with independent junctions control using hybrid tunnel junction (TJ). The hybrid TJ was gown by metal organic chemical vapor deposition (p + GaN) and molecular-beam epitaxy (n + GaN). Uniform blue, green and blue/green emission can be generated from different junction diodes. The peak external quantum efficiency (EQE) of the TJ blue µLEDs and green µLEDs with indium tin oxide contact is 30% and 12%, respectively. The carrier transportation between different junction diodes was discussed. This work suggests a promising approach for vertical µLEDs integration to enhance the output power of single LEDs chip and monolithic µLEDs with different emission colors with independent junction control.

Performance Enhancement of Cadmium‐Free Quantum‐Dot Light‐Emitting Diodes via Cl‐Passivated Zn1−x−ySnxMgyO Nanoparticles as Electron Transport Layers

AbstractAlthough cadmium (Cd)‐based nanocrystals have enabled high‐performance quantum‐dot light‐emitting diodes (QLEDs), their mass production is likely to be affected by environmental protection policies. Among all the potential Cd‐free candidates, Cu‐In‐Zn‐S (CIZS) nanocrystals (NCs) have attracted particular interests. Still, the performance of the corresponding LED is currently limited by imbalanced charge injection and luminescence quenching, which are both related to the ZnO‐based electron transporting layer (ETL). This work demonstrates that ZnO nanoparticles (NPs) doped with Sn, Mg (Zn1−x−ySnxMgyO), and passivated with Cl are promising to resolve the above issues. All‐solution‐processed QLEDs based on Cd‐free CIZS NCs are fabricated by using Zn0.9Sn0.1O NPs as the ETL, and the peak external quantum efficiency (EQEmax) was nearly twice that of ZnO (EQEmax = 1.74%). The main reason is that the incorporation of Sn can reduce the conductivity of ZnO by an order of magnitude. Combining the advantages of Zn0.9Sn0.1O, Zn0.8Sn0.1Mg0.1O@Cl NPs are designed by the co‐doping of Mg and Cl passivation. The EQEmax and current efficiency based on Zn0.8Sn0.1Mg0.1O and Zn0.8Sn0.1Mg0.1O@Cl as ETLs are further increased to 4.84%, 14.00 cd A−1 and 5.53%, 15.99 cd A−1, respectively. The positive effects of Mg ions can remarkably optimize energy level structure to balance charge injection, while Cl can further passivate defects. The findings offer a new guideline for developing Cd‐free light‐emitting diodes.

Modulating Narrow-Band Phosphorescence of Pt2Au4 Cluster Complexes by Differently Positioned Bis(acetylide)-Naphthalene Linkers

To modulate phosphorescent characteristics of Pt2Au4 complexes with differently positioned bis(acetylide)naphthalene as a bridging ligand, four isomeric Pt2Au4 complexes (1–4) linked by 1,4-bis(acetylide)naphthalene (1), 1,5-bis(acetylide)naphthalene (2), 2,6-bis(acetylide)naphthalene (3), and 2,7-bis(acetylide)naphthalene (4) are elaborately designed and prepared. The Pt2Au4 complexes are strongly phosphorescent with the quantum yields as high as 52% in CH2Cl2 solutions, in strikingly contrast to weak phosphorescence of bis(acetylide)naphthalene-linked Pt2 precursors. After the formation of Pt2Au4 cluster structures, the increased molecular rigidity dramatically suppresses nonradiative relaxation, which becomes less competitive in contrast to the radiative relaxation of the emitting state, thus resulting in a remarkable enhancement of the quantum yields. Depending on the positions of bis(acetylide) groups attached to naphthalene rings, the phosphorescence of Pt2Au4 isomers in CH2Cl2 solutions follows 1 (640 nm) → 2 (582 nm) → 3 (567 nm) → 4 (529 nm) to show progressive blue shifts. As demonstrated by photophysical and theoretical studies, vibronic-structured narrow-band emission with a full width at half maxima (fwhm) of 707–1073 cm–1 is primarily ascribable to ligand-centered triplet states localized at bis(acetylide)naphthalenes, which is dramatically activated upon the formation of the Pt2Au4 cluster because the energy harvested by two PtAu2 cluster moieties is effectively transferred to bridging bis(acetylide)naphthalene. Taking advantage of Pt2Au4 complexes 1–4 as phosphorescent emitters, solution-processed OLEDs achieve narrow-band electroluminescence with peak external quantum efficiency of 11.0% for red-emitting complex 1 (fwhm = 45 nm or 1058 cm–1), 9.4% for orange-emitting complex 2 (fwhm = 33 nm or 960 cm–1), 13.7% for yellow-emitting complex 3 (fwhm = 33 nm or 1029 cm–1), and 15.2% for green-emitting complex 4 (fwhm = 24 nm or 848 cm–1).

Control of n-Phase Distribution in Quasi Two-Dimensional Perovskite for Efficient Blue Light-Emitting Diodes.

Pure-bromide quasi-2D perovskite (PBQ-2DP) promises high-performance light-emitting diodes (LEDs), while a challenge remains on control over its n-phase distribution for bright true-blue emission. Present work addresses the challenge through exploring the passivation molecule of amino acid with reinforced binding energy, which generates narrow n-phase distribution preferentially at n = 3 with true blue emission at 478 nm. Consequently, a peak external quantum efficiency of 5.52% and a record brightness of 512 cd m-2 are achieved on the PBQ-2DP-based true blue PeLED, these both values located among the top in the records of similar devices. We further reveal that the electron-phonon coupling results in the red-shifted emission in the PBQ-2DP film, suggesting that the view of n-phase distribution dominated true-blue emission in PBQ-2DP needs to be revisited, pointing out a guideline of electron-phonon coupling suppression to relieve the strait of realizing true blue or even deep blue emission in the PBQ-2DP film.

Understanding the Role of Small Cations on the Electroluminescence Performance of Perovskite Light‐Emitting Diodes

AbstractThe delicate engineering of monovalent cations in perovskite material has led to continuous performance breakthroughs and stability improvement for the perovskite light‐emitting diodes (PeLEDs). However, the exact role of A‐site cations on the electroluminescence (EL) performance and degradation mechanism of PeLEDs has not been systematically answered yet. Herein, it is demonstrated that the most commonly used methylammonium cation (MA+) has an adverse effect on the electrochemical reaction at the interface between perovskite and metal‐oxide layer, leading to deteriorated EL performance as compared to that of the formamidinium cation (FA+)‐based perovskite. It reveals that the accelerated deprotonation process of MA+ under an electric field will aggravate the reaction between iodide and metal ion in oxide layer. The further substitution of a small portion of FA+ with inorganic cesium cation (Cs+) results in much enhanced crystallinity and enlarged crystal size, leading to an optimized peak external quantum efficiency of 21.3%. The ion migration process in the PeLEDs can be significantly suppressed with Cs+ incorporation, leading to a smaller roll‐off under large current density and an elongated half‐lifetime of 190.1 h under a current density of 20 mA cm‐2, representing one of the most stable PeLEDs based on 3D perovskite layer.