Single‐Crystal Perovskite Light‐Emitting Diodes with External Quantum Efficiency of over 8% Enabled by Nonstoichiometric Composition Tuning

Abstract

Perovskite single crystals (SCs) have been emerging as promising materials for electroluminescence (EL) device applications owing to their superior optoelectronic properties. However, the device performance of single-crystal perovskite light-emitting diodes (SC-PeLEDs) is limited by the lack of effective defect management and energy level modulation. Here, a nonstoichiometric composition tuning (NCT) strategy for the construction of high-performance SC-PeLEDs is reported. The NCT strategy, finely tuning the MABr (MA + = CH 3 NH 3 + ) excess in the nonstoichiometric MAPbBr 3 SCs to enhance the crystal quality, reduce the trap density, and elevate the energy level of the resultant perovskite SC, enables markedly decreased nonradiative recombination and more efficient carrier injection for the devices. In consequence, the optimized SC-PeLEDs exhibit an ultrahigh peak luminance of 161 900 cd m −2 and a large external quantum efficiency (EQE) of up to 8.1%, representing the most efficient SC-PeLED reported thus far. This strategy also shows a high universality in enhancing the EL performance of other lead bromide perovskite SC-PeLEDs, endowing them with luminances and EQEs three times larger than those of the pristine devices. This work opens an avenue for the development of high-performance EL devices based on perovskite SCs.

Spectrally Stable Deep-Blue Light-Emitting Diodes Based on Layer-Transferred Single-Crystalline Ruddlesden–Popper Halide Perovskites

“…44 The strong temperature dependency in the RPPbased PeLED suggests that the Joule heating must be minimized for realizing the full potential of single-crystalline RPPs, to catch up the unprecedented device lifetime of the single-crystalline 3D PeLEDs. 60,61 Efficient carrier injection under lower voltage bias conditions is highly desirable to maintain PeLEDs at lower temperatures during operation. Proper band alignment across the charge transport layers and RPPs as well as ligand engineering of RPPs to reduce the electrical resistance in the out-of-plane orientation is expected to lead to further suppression of Joule heating and improved stability.…”

“…Nevertheless, the device exhibited remarkable spectral stability in the EL over a duration of 382 s because the Joule heating was suppressed to a temperature of 350 K. As shown in Figure f, the sharp EL peak at 440 nm remains intact for over 6 min, without any broadening or the appearance of additional peaks, which was observed in the temperature-dependent PL measurement at temperatures higher than 353 K. The suppressed Joule heating of our devices is attributed to the conformal coverage of the device active area by the transferred single-crystalline, single-domain RPP layer possessing a flat surface morphology unprecedented in the previous reports on PeLEDs . The strong temperature dependency in the RPP-based PeLED suggests that the Joule heating must be minimized for realizing the full potential of single-crystalline RPPs, to catch up the unprecedented device lifetime of the single-crystalline 3D PeLEDs. , Efficient carrier injection under lower voltage bias conditions is highly desirable to maintain PeLEDs at lower temperatures during operation. Proper band alignment across the charge transport layers and RPPs as well as ligand engineering of RPPs to reduce the electrical resistance in the out-of-plane orientation is expected to lead to further suppression of Joule heating and improved stability.…”

Alkali metal salt-assisted crystal structure switch of hybrid indium halides with near-unity photoluminescence quantum yield

“…These lead halide perovskite nanocrystals possess tunable bandgaps, high defect tolerance, tunable spectra from the visible to near-infrared range, and high-efficiency luminescence, among other advantages. 1–7 Furthermore, researchers have developed various synthesis and control methods, including morphology control, surface passivation, and ion doping, to reduce the defect density in nanocrystals and achieve efficient luminescence. 8–13 Despite extensive optimization of APbX 3 perovskite nanocrystals, their luminescence is still affected by factors such as reduced PLQY due to nanocrystal aggregation and poor stability, which greatly hinder their further application in optoelectronic devices.…”