Enhanced Carrier Lifetimes of Pure Iodide Hybrid Perovskite via Vapor-Equilibrated Re-Growth (VERG).

Abstract

Solution deposition of planar films of the hybrid perovskite (HP) methylammonium (MA) lead iodochloride (MAPbI3-xClx) often results in very low surface coverage, small grain size, and high density of defects, particularly for the pure iodide HP. These decrease the optoelectronic quality of MAPbI3 (minority lifetimes all less than 10 ns) and creates pinholes that may result in shunt pathways that severely degrade the efficiency of photovoltaic devices. The poor morphology is usually attributed to the formation of large disconnected grains of PbI2 that nucleate first and set the morphology of the final HP layer. As a result, many use PbCl2 as a lead source. The PbCl2 is less soluble, forms smaller grains, and promotes more continuous HP films. Here, we show a highly reproducible deposition method for pure iodide MAPbI3 that yields continuous films with large grain sizes and minority carrier lifetimes greater than 200 ns. The method consists of thermal evaporation of PbI2 and a post-deposition Vapor-Equilibrated Re-Growth (VERG) step at 110 °C in a closed vessel.