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.
Two nondoped blue fluorescent OLEDs based on benzonitrile-anthracene derivatives with 10.06% and 9.23% EQE and low efficiency roll-off were fabricated.
All‐inorganic perovskite has attracted much attention because of the higher stability. Many organic additives such as alkyl chain ammonium and polymers are usually introduced into perovskite to improve their performance. However, the long chain ammonium cations in perovskite may restrain the carrier transfer ability and ultimately deteriorate the performance of light‐emitting diodes (LEDs). In this work, the CsPbBr3 nanoparticles (NPs) are in situ fabricated by the synergistic effect of poly(ethylene oxide) and phenethylammonium bromide (PEABr). Particularly, sodium bromide (NaBr) with better conductivity is successfully introduced into CsPbBr3 NPs to substitute PEA partially, ultimately to passivate the defect and promote the carrier transfer ability. Besides, the addition of NaBr results in a better promotion for electron mobility than for hole mobility leading to a more balanced charge transport in devices. It enables NaBr based CsPbBr3 NPs green LEDs to exhibit a maximum external quantum efficiency (EQEmax) of 17.4%, which presents obvious enhancement compared to the LEDs without NaBr (EQEmax = 12%). Further, NaBr based CsPbBr3 NPs LEDs with a large area of 108 mm2 still show a high maximum EQE of 10.2%. Above all, this work provides a feasible way of adding metal additive in perovskite films to improve the performance of perovskite LEDs.
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