Sodium Ion Modifying In Situ Fabricated CsPbBr3 Nanoparticles for Efficient Perovskite Light Emitting Diodes

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 (EQE(max)) of 17.4%, which presents obvious enhancement compared to the LEDs without NaBr (EQE(max) = 12%). Further, NaBr based CsPbBr3 NPs LEDs with a large area of 108 mm(2) 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.