Atmospheric Humidity Underlies Irreproducibility of Formamidinium Lead Iodide Perovskites.

Metal halide perovskite solar cells (PSCs) are infamous for their batch-to-batch and lab-to-lab irreproducibility in terms of stability and performance. Reproducible fabrication of PSCs is a critical requirement for market viability and practical commercialization. PSC irreproducibility plagues all levels of the community; from institutional research laboratories, start-up companies, to large established corporations. In this work, we unravel the critical function of atmospheric humidity to regulate the crystallization and stabilization of formamidinium lead triiodide (FAPbI 3 ) perovskites. We demonstrate that the humidity content during processing induces profound variations in perovskite stoichiometry, thermodynamic stability, and optoelectronic quality. Almost counterintuitively, we show that the presence of humidity is perhaps indispensable to reproduce phase stable and efficient FAPbI 3 -based PSCs. This article is protected by copyright. All rights reserved.