Short-Chain Acid Additives to Control PbI2 Crystallization in Hybrid Perovskite Films

The quality and the performance of hybrid perovskite (HP)'s films strongly depend on the complete conversion into MAPbI(3) of a spin-coated solution of methylammonium iodide (MAI) and PbI2. Highly crystalline PbI2 on a substrate limits such a conversion and, consequently, the HP's solar cell performances. We investigate for the first time the use of short-chain organic acids as additives in a non-complexing solvent like gamma-butyrolactone (GBL), that can retard retard the crystallization of PbI2. Based on XRD analyses of the spin coated films, the acetic acid is the most effective additive in retarding the PbI2 crystallization, making Pb2+ available for a subsequent reaction with MAI. These results open a new experimental path for fabricating perovskite films by single or sequential step methods involving acid additives.