Precursor non-stoichiometry to enable improved CH₃NH₃PbBr₃ nanocrystal LED performance

High photoluminescence quantum yields and narrow emission wavelengths, combined with low temperature solution processing, make CH₃NH₃PbBr₃ nanocrystals (NCs) favorable candidates for light-emitting applications. Herein, we describe the synthesis of CH₃NH₃PbBr₃ NC inks by a convenient room-temperature ligand assisted reprecipitation protocol. We further investigate the effect of modulation of the CH₃NH₃Br : PbBr₂ ratio during NC synthesis on the optical properties, crystallinity, particle size distribution and film formation of the NC ink. Subsequently, we fabricate LEDs using these NCs as the emissive layer and the highest efficiency (1.75% external quantum efficiency) and brightness (>2700 cd m^-2) is achieved for the 1.15 : 1 precursor ratio. It is inferred that the NC surface properties and film coverage are more crucial than the photoluminescence intensity to achieve high device efficiency. Moreover, by separating the NC synthesis and thin film formation processes, we can exert more control during device fabrication, which makes it very promising for scale-up applications.