Efficient quasi‐2D‐structure perovskite light‐emitting diodes (4.90 cd A−1) are demonstrated by mixing a 3D‐structured perovskite material (methyl ammonium lead bromide) and a 2D‐structured ...perovskite material (phenylethyl ammonium lead bromide), which can be ascribed to better film uniformity, enhanced exciton confinement, and reduced trap density.
Owing to unique potential for high color purity luminance based on low-cost solution processes, organic/inorganic hybrid perovskite light-emitting diodes (PeLEDs) are attracting a great deal of ...research attention. For high performance PeLEDs, optimum control of the perovskite film morphology is a critical parameter. Here, we introduce a reliable and well-controllable PeLED crystallization process based on beam-damage-free near-infrared laser (λ = 808 nm) irradiation. Morphology of the CH3NH3PbBr3 films can be precisely controlled by laser irradiation condition parameters: power density and beam scan rate. We systematically investigate the perovskite film morphology and device performance of the PeLEDs under different processing conditions. In the optimum power density and high beam scan rate (30 W cm–2, 0.1 mm s–1), a dense and smooth perovskite film is attained with a small crystal grain size. The critical relationship between the crystal grain size and LED efficiency is established while attaining the device performance of 0.95 cd A–1 efficiency and 1784 cd m–2.
Despite the ability to precisely tune their bandgap energies, mixed halide perovskites (MHPs) suffer from significant spectral instability, which obstructs their utilization for the rational design ...of light-emitting diodes. Here, we investigate the origin of the electroluminescence peak shifts in layered MHPs containing bromide and iodide. X-ray diffraction and steady-state absorption measurements prove effective integration of iodide into the cubic lattice and the spatially uniform distribution of halides in the ambient environment. However, the applied electric field during the device operation is found to drive the systematic halide migration. Quantum mechanical density functional theory calculations reveal that the different activation energies required for directional ion hopping lead to the redistribution of anions. In-depth analyses of the electroluminescence spectra indicate that the spectral shifting rate is dependent on the drift velocity of halides. Finally, it is suggested from our study that the dominant red emission is ascribed to the thermodynamically favorable selective hole injection. Our mechanistic study provides insights into the fundamental reason for the spectral instability of devices based on MHPs.
Organic-inorganic halide perovskite light emitting diode (PeLED) as a narrow band emitter is an emerging research field. To overcome limited electroluminescence efficiency of PeLEDs, trap-assisted ...non-radiative recombination in polycrystalline perovskite films should be reduced and the electron-hole balance in the PeLEDs must be improved. In this work, we investigated a practical way to effectively overcome above-mentioned issues by unravelling additive-based nanocrystal pinning (A-NCP) process using the carefully controlled electron transporting organic material solutions diluted in a volatile non-polar solvent. We found that without affecting the intrinsic crystal structure, A-NCP improved the radiative recombination rate by reducing effective defect density at grain boundaries due to the defect healing effect. Moreover, it induced the improved electron-hole balance in the dominantly p-type CH3NH3PbBr3 based PeLEDs, leading to the highest efficiency of 8.79% ever reported to date among organic-inorganic halide perovskite-based green PeLEDs. Therefore, our work gives the effective approaches for efficient PeLEDs from the investigations of the role of A-NCP incorporating a tiny amount of an electron transporting molecule as an additive to increase radiative recombination rate of polycrystalline perovskite films.
Mechanism and effects of additive-based nanocrystal pinning process are investigated for highly efficient organic-inorganic halide perovskite light-emitting diodes. Display omitted
•The effects of additive-based nanocrystal pinning process is systematically investigated.•Grain size effect, defect healing effect, and improvedelectron injection are investigated.•We achieved the highest device efficiency of 8.79% among OHP-based PeLEDs.
We report ultrafast recrystallization of perovskite (methylammonium lead tribromide, MAPbBr3) by flash light annealing (FLA) for light-emitting diode (LED) application. Intense near-infrared (NIR) ...peak spectrum (830 and 900 nm) of flash light could rapidly heat MAPbBr3 based LED structures over ∼320 °C without radiative damage. Cuboidal morphology of the perovskite active layer was evolved into the dense recrystallized structure with a noticeably small grain size (∼38 nm) by FLA, which significantly promoted the radiative recombination. Surface roughness (root mean square (RMS)) of the perovskite layer was decreased by 62% (from 8.47 to 3.22 nm) via FLA, while inhibiting the leakage current that limit current efficiency (CE) of perovskite LED (PeLED). Three dimensional temperature simulation was investigated for the mechanism of flash-induced MAPbBr3 recrystallization. Finally, FLA was successfully exploited for the flexible PeLEDs on polyethylene naphthalate substrates, which exhibited 252% larger CE compared to thermally annealed counterpart.
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•Ultrafast recrystallization of perovskite is demonstrated by flash light annealing (FLA).•Cuboidal MAPbBr3 was transformed into dense film with small grain size down to ~38 nm and smooth surface by FLA.•Current efficiency of MAPbBr3 light emitting diode was enhanced by 263% via FLA compared with thermally annealed counterpart.
Perovskite nanocrystals are promising luminescent materials with synthetic feasibility and band gap tunability. Nonetheless, application of the perovskite nanocrystals to light-emitting devices has ...been challenging because of the intrinsic poor colloidal stability and environmental vulnerability issues. Here, we introduce a new protocol for highly air-stable perovskite nanocrystal layers with a tunable band gap via a simple nanocrystal pinning process. The nanocrystals were composed of CH3NH3PbBr3 (MAPbBr3) mixed with (vinylbenzylamine)2PbBr4 ((VBzA)2PbBr4), which contains a photopolymerizable structure-directing ligand. Along with the compostion of (VBzA)2PbBr4, the band gap of the perovskite layer continuously increased with the reduction of the nanocrystal size and also lattice distortion. The nanocrystal film readily polymerized upon exposure to visible light was highly stable under humid air more than 15 days. Its application to bluish-green light-emitting diodes is demonstrated.
Interfacial engineering of organic–inorganic halide perovskites in conjunction with different functional materials is anticipated to offer novel heterojunction structures with unique functionalities. ...Unfortunately, complex material compositions and structures of the organic–inorganic hybrid materials make it difficult to tailor a desirable intermolecular interaction at the interface. Spontaneous and highly specific nucleation of perovskite crystals, that is, methylammonium lead iodide perovskite (CH3NH3PbI3, MAPbI3) at nitrogen‐doped carbon nanotube (NCNT) surfaces for the self‐assembly of MAPbI3/NCNT hybrids is reported. It is demonstrated that the lone‐pair electrons of pyridinic nitrogen‐dopant sites at NCNTs mediate specific interactions with the cationic component in the perovskite structure and serve as the nucleation sites via coordinate bonding formation, as supported by X‐ray photoelectron spectroscopy and density functional theory calculation. The potential suitability of MAPbI3/NCNT hybrids is presented for highly sensitive and selective NO2 sensing layer. This work suggests a reliable self‐assembly route to the molecular level hybridization of organic–inorganic halide perovskites by employing the substitutional dopant sites at graphene‐based nanomaterials.
The specific nucleation site and interfacial interaction between methylammonium lead iodide perovskite (CH3NH3PbI3, MAPbI3) and nitrogen‐doped carbon nanotube (NCNT) are demonstrated by experimental and theoretical analysis. The methylammonium ion is modified by sharing a proton with a pyridinic N‐dopant site for interfacial interaction. The MAPbI3/NCNT hybrids exhibit sensitive and selective NO2 sensing activities.
Efficient quasi‐2D perovskite light‐emitting diodes (PeLEDs) are realized by partially substituting methyl ammonium (MA) cations with phenylethyl ammonium cations in MAPbBr3. The excitons move to the ...crystals, which have the smallest bandgap, and recombine. The quasi‐2D PeLED designed by T.‐W. Lee and co‐workers, as described on page 7515, shows higher luminance and current efficiency (2935 cd m−2 and 4.90 cd A−1, respectively) compared with 3D MAPbBr3 PeLEDs.
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