Enhanced performance of perovskite solar cells by modulating the Lewis acid-base reaction

The Lewis acid-base reaction between PbI₂ and solvent molecules is popular in fabricating PbI₂ films by a two-step method for making perovskite solar cells. Here, we control the microstructure of PbI₂ films through modulating the Lewis acid-base reaction by adding a small amount of N-methyl pyrrolidone into PbI₂/DMF solution. PbI₂ films with excellent crystallinity and full coverage are fabricated by spin-coating the mixed solution on the substrate, which leads to high quality perovskite layers with low recombination rate and high efficiency for carrier transfer. As a result, the power conversion efficiency of the best perovskite solar cells increases from 13.3% to 17.5%.