N-Methyl-2-pyrrolidone as an excellent coordinative additive with a wide operating range for fabricating high-quality perovskite films

Abstract

We demonstrate in this work that N-methyl-2-pyrrolidone (NMP) is a superior alternative to dimethyl sulfoxide (DMSO) as an additive in a precursor solution for the fabrication of high-quality perovskite films for solar cells. While the DMSO-assisted method always requires the films to be prepared with a low and restricted PdI₂ : DMSO ratio, NMP provides a much wider window of the PbI₂/NMP ratio for the preparation of high-quality perovskite films. The systematic studies on the structures of intermediates obtained with different PbI₂/NMP ratios reveal that only one kind of intermediate forms regardless of the Pb²⁺/NMP ratio between 1 and 4, which is totally different from the situation of a PbI₂/DMSO system. But all the perovskite solar cell devices fabricated with different Pb²⁺/NMP ratios show similar performances to their counterpart fabricated with 1 : 1 Pb²⁺/DMSO. Besides the MAPbI₃ (MA = CH₃NH₃⁺) system, NMP is shown to be an excellent coordinative additive for the fabrication of high-quality triple-cation (Cs⁺/formamidinium/MA) perovskite films.