High‐Efficiency Formamidinium Lead Bromide Perovskite Nanocrystal‐Based Light‐Emitting Diodes Fabricated via a Surface Defect Self‐Passivation Strategy

Abstract

Formamidinium lead bromide (FAPbBr3) nanocrystals (NCs) demonstrate great potential in light‐emitting diode (LED) applications due to their pure green emission and excellent stability. However, the abundant defects at the surface of the NCs act as charge trapping centers and significantly increase the trap‐assisted nonradiative recombination channels, hampering the performance improvement of LEDs based on FAPbBr3 NCs. Herein, a facile self‐passivation strategy of the surface defects is developed by introducing excess formamidinium bromide (FABr) during the colloidal synthesis of NCs, leading to much improved photoluminescence quantum yield (PLQY) of the obtained NCs. In addition, enhanced charge transport property is measured in the assembled films owing to the simultaneously declined insulating ligands at the surface of NCs. The molar ratio of FABr and PbBr2 is rationally optimized during the synthesis of NCs and high‐efficient green‐emissive LEDs are fabricated with a champion current efficiency of 76.8 cd A−1, corresponding to an external quantum efficiency of 17.1%, which is among the best‐performing green LEDs based on perovskite NCs so far.

Ion Migration in Perovskite Light‐Emitting Diodes: Mechanism, Characterizations, and Material and Device Engineering

“…By contrast with perovskite photovoltaic devices that generally have stoichiometric precursors, the fabrication of PeLEDs typically uses excess halide salts (AX) to passivate defects, [59][60][61] modulate film crystallization (decrease crystallite size, [62,63] eliminate the non-perovskite δ-phase, [64] and create island morphology beneficial for light out-coupling [65,66] ), tune band alignment, [67] and balance charge injection [1] and prevent leakage current. [65,66] In our previous work, we demonstrated that after the film formation, excess FAI derived from perovskite precursors still exist at grain boundaries and in the gaps between island grains (Figure 2c).…”

Elucidation of the structural and optical properties of metal cation (Na+, K+, and Bi3+) incorporated Cs2AgInCl6double perovskite nanocrystals

“…5–10 Light emitting diodes and solar cells based on these metal halide perovskites have shown excellent performance with efficiencies of nearly 25% power conversion efficiency (PCE) of solar cells and 20% external quantum efficiency (EQE) of LEDs. 4,11–19 However, these families of perovskites contain Pb which limits the commercial viability of these materials due to its environmental incompatibility and toxicity. 17 The subsequent development of Pb-free perovskite systems has been extensive; however, the performance of these materials is inferior to their Pb-containing analogues.…”

Lead Halide Perovskite Nanocrystals: Room Temperature Syntheses toward Commercial Viability

“…Shortly after this paper, there followed several other LARP syntheses of MAPbX 3 and FAPbX 3 NCs, following similar protocols. [49][50][51][52] However, the thermal and environmental stability of these materials are compromised by their volatile organic cations. [53,54] All-inorganic CsPbX 3 typically offers much higher stability, and therefore represents a far more realistic option for commercial applications.…”