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 MAPbI3 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 ?-butyrolactone (GBL), able to retard the crystallization of PbI2. By XRD analyses on the spin-coated films, the acetic acid results to be 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.