Perovskite Light-emitting Diodes Research Articles

Regulated Perovskite Crystallization for Efficient Blue Light‐Emitting Diodes via Interfacial Molecular Network

AbstractMetal halide perovskite light‐emitting diodes (PeLEDs) are gaining increasing attention as a promising candidate for the new‐generation display technology. Although tremendous progress has been witnessed in this field, the device performance of blue PeLEDs still lags far behind that of the green and red counterparts. In this work, an effective interfacial engineering is employed to boost the radiative recombination of blue perovskite film by introducing a multifunctional tetraethyl orthosilicate (TEOS) network on the grain‐growth substrate. Benefitting from the strong interaction between the TEOS molecule and perovskite nuclei, the perovskite crystallization dynamics are effectively regulated, contributing to significantly improved emitting film with uniformly distributed halogen and concentrated low‐dimensional domain. Additionally, the TEOS network can distinctly passivate the crystal defects at the buried perovskite interface owing to its adequate electron‐donating sites. Consequently, the target blue PeLEDs featuring a stable emission peak at 488 nm exhibit a champion external quantum efficiency of 17.3%, which is among the highest values to date. The results demonstrate the critical role of the surface molecular characteristics of the grain‐growth substrate in regulating the mixed‐halide blue perovskite crystallization.

Strongly-Confined CsPbBr3 Perovskite Quantum Dots with Ultralow Trap Density and Narrow Size Distribution for Efficient Pure-Blue Light-Emitting Diodes.

The development of pure-blue perovskite light-emitting diodes (PeLEDs) faces challenges of spectral stability and low external quantum efficiency (EQE) due to phase separation in mixed halide compositions. Perovskite quantum dots (QDs) with strong confinement effects are promising alternatives to achieve high-quality pure-blue PeLEDs, yet their performance is often hindered by the poor size distribution and high trap density. A strategy combining thermodynamic control with a polishing-driven ligand exchange process to produce high-quality QDs is developed. The strongly-confined pure-blue (≈470nm) CsPbBr3 QDs exhibit narrow size distribution (12% dispersion) and are achieved in Br-rich ion environment based on growth thermodynamic control. Subsequent polishing-driven ligand exchange process removes imperfect surface sites and replaces initial long-chain organic ligands with short-chain benzene ligands. The resulting QDs exhibit high photoluminescence quantum yield (PLQY) to near-unity. The resulting PeLEDs exhibit a pure-blue electroluminescence (EL) emission at 472nm with narrow full-width at half-maximum (FWHM) of 25nm, achieving a maximum EQE of 10.7% and a bright maximum luminance of 7697cdm-2. The pure-blue PeLEDs show ultrahigh spectral stability under high voltage, a low roll-off of EQE, and an operational half-lifetime (T50) of 127min at an initial luminance of 103cdm-2 under continuous operation.

Crown-Assisted CsCu2I3 Growth and Trap Passivation for Perovskite Light-Emitting Diodes.

Copper (Cu)-based perovskites are promising for lead-free perovskite light-emitting diodes (PeLEDs). However, it remains a significant challenge to achieve high performance devices due to the nonradiative loss caused by the disordered crystallization and lack of passivation. Crown ethers are known to form host-guest complexes by the interaction between C-O-C groups and certain cations, and 18-crown-6 (18C6) with an appropriate complementary size can interact with Cs+ and Cu+ cations. Herein, we studied the interaction between CsCu2I3 and two crowns with the same cyclic size, 18C6 and dibenzo-18-crown-6 (D18C6). Particularly, D18C6 can reduce the nonradiative recombination rate of CsCu2I3 film by passivating the defects and optimizing the film morphology effectively. The room mean square (RMS) decreased from 5.06 to 2.95 nm, and the PLQY was promoted from 4.71% to 19.9%. Besides, D18C6 can also decrease the barrier of hole injection. The PeLEDs based on D18C6-modified CsCu2I3 realized noticeable improvement with a maximum luminance and EQE of 583 cd/m2 and 0.662%, respectively.

Bi‐Functional Chelating Ligand Enables Ultra‐Stable Blue Emissive CsPbBr3 Nanoplatelets Film

AbstractQuantum‐confined perovskite CsPbBr3 Nanoplatelets (NPLs) have recently emerged as promising blue‐emitting materials for perovskite light‐emitting diodes (PeLEDs). Yet, their susceptibility to optical instability in solid films under ambient conditions poses a significant hindrance. This study introduces a novel chelating strategy that utilizes metal manganese ions and multidentate ligands, markedly improving the structural stability, and emission efficiency of NPLs. The approach involves adding Diethylenetriaminepentaacetic acid (DTPA) to the perovskite precursor solution, which allows for strong coordination to surface [PbBr6]4− octahedrons via its multiple chelation sites. Ensuing metal manganese ion integration during the purification phase addresses Pb2+ and Br− site vacancies, culminating in near‐perfect octahedral structures with significantly fewer vacancies. These metal manganese ions are then further immobilized on the NPLs surface by the chelating effect of unbound DTPA functional groups. The resultant CsPbBr3 NPLs films demonstrate an impressive PLQY of 66%, showcasing remarkable air stability with consistent blue emission for up to 5 days. The CsPbBr3 NPLs‐based PeLEDs show electroluminescence at 460 nm with a current efficiency of 1.07 cd A−1 and a maximum luminance of 220 cd m−2. The proposed chelating strategy positions perovskite NPLs as an extremely promising prospect in future applications of high‐definition displays and high‐quality lighting.

A multifunctional display based on photo-responsive perovskite light-emitting diodes

AbstractCurrent display screens are typically only used for information display, but can have a range of different sensors integrated into them for functions such as touch control, ambient light sensing and fingerprint sensing. Photo-responsive light-emitting diodes (LEDs), which can display information and respond to light excitation, could be used to develop future ultra-thin and large screen-to-body ratio screens. However, photo-response is difficult to achieve with conventional display technologies. Here, we report a multifunctional display that uses photo-responsive metal halide perovskite LEDs as pixels. The perovskite LED display can be simultaneously used as a touch screen, ambient light sensor and image sensor (including for fingerprint drawing) without integrating any additional sensors. The light-to-electricity conversion efficiency of the pixels also allow the display to act as a photovoltaic device that can charge the equipment.

Co‐Interlayer Engineering for Homogenous Phase Quasi‐2‐D Perovskite and High‐Performance Deep‐Blue Light‐Emitting Diodes

AbstractOrganic and inorganic hybrid perovskites are a class of solution‐processable semiconductors that hold significant promise for light‐emitting diode applications. However, the development of efficient blue perovskite light‐emitting diodes (PeLEDs) has remained a critical challenge. Although significant advancements have been achieved in the development of sky‐blue PeLEDs, the performance of pure‐blue and deep‐blue PeLEDs still lags. In this manuscript, by incorporating 1‐cyclohexene‐1‐ethanamine cation (CEA+) into the host 1‐phenylbutylamine cation (PBA+) spacer and fabricating mixed‐cations quasi‐2D perovskites, a homogeneous phase distribution in quasi‐2D perovskite films is achieved through precise tuning of the phase formation energy. The resulting PeLEDs exhibit remarkable performance with an external quantum efficiency (EQE) of 5.8% at 467 nm, which is one of the highest EQEs among the deep‐blue light quasi‐2D PeLED devices with emission wavelengths below 470 nm, Additionally, the device demonstrates a half‐lifetime of ≈ 25 min. Furthermore, the PeLEDs utilizing mixed‐cation perovskite exhibit a stable electroluminescence (EL) spectrum under varying voltage biases, even when the chlorine content in the halogen sites reaches as high as 30%. Overall, this work offers a novel and promising avenue to achieve both high EQE and a stable EL spectrum in blue‐light quasi‐2D PeLEDs.

Metal Halide Perovskite Light-Emitting Devices for Optical Communications: A Spotlight on Speed, Brightness, Wavelength Tunability, Bidirectionality, and Integration

Metal Halide Perovskite Light-Emitting Devices for Optical Communications: A Spotlight on Speed, Brightness, Wavelength Tunability, Bidirectionality, and Integration

Regulating Surface-Passivator Binding Priority for Efficient Perovskite Light-Emitting Diodes.

Suppressing trap-assisted nonradiative losses through passivators is a prerequisite for efficient perovskite light-emitting diodes (PeLEDs). However, the complex bonding between passivators and perovskites severely suppresses the passivation process, which still lacks comprehensive understanding. Herein, the number, category, and degree of bonds between different functional groups and the perovskite are quantitatively assessed to study the passivation dynamics. Functional groups with high electrostatic potential and large steric hindrance prioritize strong bonding with organic cations and halides on the perfect surface, leading to suppressed coordination with bulky defects. By modulating the binding priorities and coordination capacity, hindrance from the intense interaction with perfect perovskite is significantly reduced, leading to a more direct passivation process. Consequently, the near-infrared PeLED without external light out-coupling demonstrates a record external quantum efficiency of 24.3% at a current density of 42mA cm-2. In addition, the device exhibits a record-level-cycle ON/OFF switching of 20000 and ultralong half-lifetime of 1126.3h under 5mA cm-2. A deep understanding of the passivators would offer new insights into the development of high-performance PeLEDs. This article is protected by copyright. All rights reserved.

Alkoxysilane‐Treated SnO2 Interlayer for Energy Band Alignment of SnO2 Electron Injection Layer in Inverted Perovskite Light‐Emitting Diodes

AbstractEfficient inverted perovskite light‐emitting diodes (PeLEDs) are demonstrated by the introduction of tetraethyl orthosilicate (TEOS)‐incorporated tin oxide (SnO2) interlayer between the SnO2 electron injection layer and the perovskite emission layer. The TEOS incorporation into the SnO2 solution spontaneously converts it to a SiO2–SnO2 composite colloidal solution with a wide band gap, thermal stability, transparency, and chemical stability toward perovskite. The TEOS‐incorporated SnO2 interlayer effectively restricts the charge transfer from perovskite into SnO2 and promotes electron injection from SnO2 into perovskite due to the shift toward favorable energy band alignment. In addition, the TEOS‐treated interlayer balances the electron injection rate and the hole injection rate, thereby facilitating radiative recombination of the charge carriers injected into perovskite. As a result, the inverted PeLEDs exhibit significantly improved performance of 33 996 cd m−2 luminance, 9.99% of external quantum efficiency, and 44.83 cd A−1 of current efficiency.

Advancements in the improvement of optical outcoupling efficiency for perovskite LEDs

Advancements in the improvement of optical outcoupling efficiency for perovskite LEDs

Double Passivation Using Ultra‐Thin Insulators for Improved Stability and Efficiency of Quasi‐2D Perovskite Light Emitting Diodes

AbstractInterface engineering is a critical parameter for optimal optoelectronic device performance. In quasi‐2D perovskite light emitting diodes (PeLEDs), traditional poly (3,4‐ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) hole injection layer (HIL) is replaced by self‐assembled monolayer (SAM) [2‐(3,6‐dibromo‐9H‐carbazol‐9‐yl) ethyl] phosphonic acid (Br‐2PACz) HIL. The deep highest occupied molecular orbital (HOMO @ −5.73 eV) of Br‐2PACz facilitates the efficient hole‐injection along with a reduction in leakage current by 4–5 orders of magnitude as compared to PEDOT:PSS (HOMO @  −5.00 eV) HIL based optimized PeLEDs. Ultra‐thin SAM‐based Br‐2PACz HIL presents two challenges: i) device reproducibility is hindered by spatial inhomogeneity, and ii) it fails to regulate nonradiative recombination at the perovskite/HIL interface. To address these challenges, the ultra‐thin interlayer of atomic layer deposited aluminum oxide (Al2O3) is utilized between Br‐2PACz, and perovskite which aids in passivating the interfacial states at the HIL/perovskite interface. With the optimized thickness of Al2O3 interlayer (3 nm), the device's external quantum efficiency (EQE) improved from 9.47% to 13.14%, accompanied by luminous efficiency of 42.8 cd A−1. An ultra‐thin interlayer of lithium fluoride (LiF) (2 nm) is implemented on the top side of the perovskite, which can provide 1.5 times increase in the device's LT50 stability.

Controlling Interfacial Amidation Reaction Rate to Regulate Crystal Growth toward High-Performance FAPbBr3-Based Inverted Light-Emitting Diodes.

Controlling interfacial reactions is critical for zinc oxide (ZnO)-based inverted perovskite light-emitting diodes (PeLEDs), boosting the external quantum efficiency (EQE) of the near-infrared device to above 20%. However, violent interfacial reactions between the bromine-based perovskites and ZnO-based films severely limit the performance of inverted green PeLEDs, whose efficiency and stability lag far behind those of their near-infrared counterparts. Here, a controllable interfacial amidation between the bromine-based perovskites and magnesium-doped ZnO (ZnMgO) film utilizing caprylyl sulfobetaine (SFB) is realized. The SFB molecules strongly interact with formamidinium bromide, decelerating the amidation reaction between formamidinium and carboxylate groups on the ZnMgO film, thus regulating the crystallization of FAPbBr3. Combined with the passivation of benzylamine, a FAPbBr3 bulk film directly deposited on a ZnMgO substrate with single-crystal characteristics is obtained, exhibiting a high photoluminescence quantum yield of above 80%. The resultant PeLEDs demonstrate a peak EQE of exceeding 20% at a high luminance of 120,000 cd m-2 and a half lifetime of 26 min at 11,000 cd m-2, representing the state-of-the-art inverted green electroluminescence. This work resolves the crucial issues of violent interfacial reactions and provides a strategy toward inverted green PeLEDs with outstanding performance.

Vertically Concentrated Quantum Wells Enabling Highly Efficient Deep‐Blue Perovskite Light‐Emitting Diodes

Deep‐blue perovskite light‐emitting diodes (PeLEDs) based on quasi‐two‐dimensional (quasi‐2D) systems exist heightened sensitivity to the domain distribution. The top‐down crystallization mode will lead to a vertical gradient distribution of quantum well (QW) structure, which is unfavorable for deep‐blue emission. Herein, a thermal gradient annealing treatment is proposed to address the polydispersity issue of vertical QWs in quasi‐2D perovskites. The formation of large‐n domains at the upper interface of the perovskite film can be effectively inhibited by introducing a low‐temperature source in the annealing process. Combined with the utilization of NaBr to inhibit the undesirable n=1 domain, a vertically concentrated QW structure is ultimately attained. As a result, the fabricated device delivers a narrow and stable deep‐blue emission at 458 nm with an impressive external quantum efficiency (EQE) of 5.82%. Green and sky‐blue PeLEDs with remarkable EQE of 21.83% and 17.51% are also successfully achieved, respectively, by using the same strategy. The findings provide a universal strategy across the entire quasi‐2D perovskites, paving the way for future practical application of PeLEDs.

Vertically Concentrated Quantum Wells Enabling Highly Efficient Deep-Blue Perovskite Light-Emitting Diodes.

Deep-blue perovskite light-emitting diodes (PeLEDs) based on quasi-two-dimensional (quasi-2D) systems exist heightened sensitivity to the domain distribution. The top-down crystallization mode will lead to a vertical gradient distribution of quantum well (QW) structure, which is unfavorable for deep-blue emission. Herein, a thermal gradient annealing treatment is proposed to address the polydispersity issue of vertical QWs in quasi-2D perovskites. The formation of large-n domains at the upper interface of the perovskite film can be effectively inhibited by introducing a low-temperature source in the annealing process. Combined with the utilization of NaBr to inhibit the undesirable n=1 domain, a vertically concentrated QW structure is ultimately attained. As a result, the fabricated device delivers a narrow and stable deep-blue emission at 458 nm with an impressive external quantum efficiency (EQE) of 5.82%. Green and sky-blue PeLEDs with remarkable EQE of 21.83% and 17.51% are also successfully achieved, respectively, by using the same strategy. The findings provide a universal strategy across the entire quasi-2D perovskites, paving the way for future practical application of PeLEDs.

In-Situ passivation of mixed-halide perovskite nanocrystals for high-performance blue light-emitting diodes

In halide perovskite nanocrystals (NCs), insulating long chain ligands such as oleic acid (OA) and oleylamine (OAm) often remove the halide ions during the purification process, leading to surface vacancy defects. This hinders their application in light-emitting devices. Herein, we report an in-situ passivation strategy using ethyl trifluoroacetate, which is hydrolyzed to trifluoroacetic acid, as an antisolvent in the purification process to passivate defects by reacting with uncoordinated Pb2+ and OAm on the surface of NCs, thus anchoring Br− to the surface of NCs. This achieves a mild removal of OAm and OA while passivating both anionic and cationic vacancies. Consequently, we achieved high-performance blue perovskite light-emitting diodes (PeLEDs). The PeLEDs based on these NCs exhibit pure blue electroluminescence at 463 nm with an external quantum efficiency of 4.14 % and a luminance of 1035 cd m−2. This study provides insights and a foundation for the development of high-performance PeLEDs.

Improved performance of quasi-two dimensional perovskite light-emitting diodes with l-phenylalanine-doped PEDOT:PSS hole transport layer

Improved performance of quasi-two dimensional perovskite light-emitting diodes with l-phenylalanine-doped PEDOT:PSS hole transport layer

Reduced phonon coupling via controlled defect levels in blue emitting CsPbBr3 nanoplatelets

Metal-halide perovskites (MHPs) are promising materials for light-emitting diodes (LEDs) because of their high color purity, wide gamut, and low-cost processing. However, blue-emitting MHP LEDs exhibit low external quantum efficiencies because they are more susceptible to defect states with a larger energy bandgap compared to their green and red counterparts. Current strategies for achieving blue-emitting MHP LEDs involve compositional engineering; however, the ion migration of mixed halides imposes significant challenges related to abundant trap states. Therefore, in this study, we systematically investigated the effects of short organic and inorganic ligands with characteristic molecular structures and adjacent moieties on the optoelectronic characteristics of low-dimensional CsPbBr3 nanoplatelets (NPLs) used as blue emitters in PeLEDs. Inorganic ligand (i.e., hydrazine monohydrobromide; HZBr) treatment achieved the most significant photoluminescence enhancement (∼10 fold) while preserving crystalline morphology and colloidal stability. Temperature-dependent photophysical properties reveal that HZBr treatment eliminates band tail states arising from lower defect levels in highly confined CsPbBr3 NPLs. Therefore, it suppresses defect trapping and electron–phonon coupling, thereby reducing thermal quenching properties. The HZBr-treated NPLs were integrated into blue perovskite LEDs and demonstrated a narrow emission peak at 471 nm.

Phosphonic acid based bifunctional additive for high-performance blue perovskite light-emitting diodes

Quasi-two-dimensional (quasi-2D) Ruddlesden-Popper (RP) phase perovskite materials exhibiting quantum confinement effect are promising candidates for realizing high-performance blue perovskite light-emitting diodes (PeLEDs). However, the performance of blue PeLEDs based on quasi-2D perovskites remains unsatisfactory, as it is limited by non-ideal charge transport, energy transfer, and defect. Here, a series of bifunctional phosphonic acid additives with synergistic effects are reported. These additives passivate defects and reduce non-radiative recombination losses by coordinating PO functional group with unsaturated Pb2+, and they promote energy transfer and radiative recombination by optimizing the proportion of small n phases and large n phases. Owing to the synergistic effects of passivation and energy transfer, optimized blue PeLEDs (∼486 nm) with 3-phosphonopropionic acid (3-PA) additive exhibits a champion EQE of 13.11%, which is exceptionally high for blue PeLEDs.

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.

Interfacial Coulomb-enhanced charge injection for efficient perovskite light-emitting diodes

Unbalanced electron-hole injection in perovskite light-emitting diodes (PeLEDs) has always been a major stumbling block limiting device performance. Here we develop a heterointerface Coulomb enhancement strategy to efficiently promote electron injection between perovskite emitter and transport layer and thereby balance the electron-hole recombination equilibrium through manipulating defect-rich positive-charge centers induced Coulomb interactions in LiF interlayer. Through multiscale polarization response characterizations combined with capacitance-voltage and electrochemical impedance spectroscopy, it is confirmed that diffusing holes trapped in LiF layer leads to the increased interfacial polarization. Moreover, the polarization response reversal and high-frequency-dependent dissipation sensitivity further corroborate the LiF-induced interfacial Coulomb enhancement mechanism. The universality of the concept is also successfully verified in devices with electron-only, hole-only, and PN structures. Consequently, the modified PeLEDs show a lower leakage current, along with a significant performance improvement by 1.9 times in external quantum efficiency (18.8%) and 5.7 times in luminance compared with control samples. This study provides a unique perspective to promote carrier transport balance by taking advantage of physical effects within interlayer.