Localized exciton emission in CsPbBr3 nanocrystals synthesized with excess bromide ions

Abstract

All-inorganic perovskite nanocrystals (NCs) have recently emerged as a new class of materials due to their tunable bandgaps and high photoluminescence quantum yields (PLQYs). The origin of the enhancement of PLQY of CsPbBr₃ NCs is usually attributed to the efficient passivation of the surface halide vacancies creating nonradiative recombination sites. In this work, Br-rich CsPbBr₃ NCs with a PLQY of 97% were prepared using an extreme excess of Br source with Br/Pb of 4.5/1 from the ligand itself at room temperature. Br-rich CsPbBr₃ NC based light-emitting devices were fabricated under ambient conditions, exhibiting the maximum current efficiency of 1 cd A⁻¹ at the luminance of 750 cd m⁻². First principles calculations indicate that Br interstitials can form the strong localized states. Such localized effect can prevent photogenerated carriers from defusing to non-radiative recombination centers, thus being responsible for the high emission efficiency.