The Effect of Humidity upon the Crystallization Process of Two-Step Spin-Coated Organic-Inorganic Perovskites.

Moisture is shown to activate the reaction between PbI2 and methylammonium halides. In addition, two activating mechanisms are proposed for the formation of CH3 NH3 PbI3 and CH3 NH3 PbI3-x Clx films from a series of carefully controlled experiments. When these rapidly formed perovskite films are directly fabricated into the devices, poor photovoltaic properties are found, due to heavy surface charge recombination. However, the cell performance can be significantly enhanced to 13.63 % and to over 12 % in the steady state for CH3 NH3 PbI3 and to 15.50 % and over 14 % in the steady state for CH3 NH3 PbI3-x Clx , if the rapidly formed perovskite film is annealed. Thus, it is believed that moisture (below 60 % RH) is not a problem for the fabrication of highly efficient perovskite solar cells.