A Multifunctional "halide-Equivalent" Anion Enabling Efficient CsPb(Br/I)3 Nanocrystals Pure-Red Light-Emitting Diodes with External Quantum Efficiency Exceeding 23.

Abstract

All-inorganic perovskite nanocrystals (NCs) are promising candidates for light-emitting diodes (LEDs) owing to their excellent optoelectronic properties. However, the pure-red perovskite LEDs (PeLEDs) available today made from mixed-halide CsPb(Br/I)3 NCs suffer from a compromise in their emission efficiency and spectral stability on account of severe trap-mediated nonradiative recombination loss, halide phase segregation, and self-doping effect, all of which are caused by the surface halide vacancies. Herein, we introduced a "halide-equivalent" anion of benzenesulfonate (BS- ) into CsPb(Br/I)3 NCs as multifunctional additive to simultaneously address the above challenging issues. Joint experiment-theory characterizations reveal that the BS- can not only passivate the uncoordinated Pb2+ related defects at surface of NCs, but also increase the formation energy of halide vacancies, resulting in substantially improved optical properties and phase stability of NCs. Moreover, electrons are expected to transfer from the CsPb(Br/I)3 NC to BS- because of the strong electron-withdrawing property of sulfonate group, which reduces the self-doping effect and alters the n-type behavior of CsPb(Br/I)3 NCs to near ambipolarity for balancing carrier injection in the device. Eventually, synergistic boost in device performance is achieved for pure-red PeLEDs with Commission Internationale del'Eclairage color coordinates of (0.70, 0.30) and a champion external quantum efficiency of 23.5%, which is a record value among the ever-reported red PeLEDs approaching to the Rec. 2020 red primary color. Moreover, the BS- -modified PeLEDs demonstrates robust spectral stability, showing negligible wavelength shift under different operating voltages. This strategy paves an efficient way for improving the efficiency and stability of pure-red PeLEDs. This article is protected by copyright. All rights reserved.