Highly Emissive and Stable Organic-Perovskite Nanocomposite Thin Films with Phosphonium Passivation.

Organometal halide perovskite materials, in particular colloidal perovskite nanocrystals (NCs), have been investigated extensively as next-generation light-emitting materials. However, producing highly efficient and stable perovskite thin films from colloidal NCs is not trivial, as dissociation of surfactants often occurs during the thin-film formation. Here, we demonstrate a facile solution-processing approach to prepare perovskite nanocomposite thin films by using phosphonium as the capping ligand for methylammonium lead bromide (MAPbBr) NCs. The photoluminescence and stability of thin films containing formed perovskite NCs were greatly enhanced after phosphonium passivation, with the photoluminescence quantum efficiency reaching 78% and only 5% decrease of the intensity after one month's exposure in ambient conditions. Electrically driven light-emitting diodes (LEDs) based on pristine perovskite neat thin films and organic-perovskite nanocomposite thin films were fabricated, and we observed a 10-fold improvement in the external quantum efficiency of these LEDs (from 0.6% to 6.3%) resulting from the formation of perovskite NCs with phosphonium passivation.