Solvent Engineering Using a Volatile Solid for Highly Efficient and Stable Perovskite Solar Cells

A strategy for efficaciously regulating perovskite crystallinity is proposed by using a volatile solid glycolic acid (HOCH2COOH, GA) in an FA(0.85)MA(0.15)PbI(3) (FA: HC(NH2)(2); MA: CH3NH3) perovskite precursor solution that is different from the common additive approach. Accompanied with the first dimethyl sulfoxide sublimation process, the subsequent sublimation of GA before 150 degrees C in the FA(0.85)MA(0.15)PbI(3) perovskite film can artfully regulate the perovskite crystallinity without any residual after annealing. The improved film formation upon GA modification induced by the strong interaction between GA and Pb2+ delivers a champion power conversion efficiency (PCE) as high as 21.32%. In order to investigate the role of volatility in perovskite solar cells (PSCs), nonvolatile thioglycolic acid (HSCH2COOH, TGA) with a similar structure to GA is utilized as an additive reference. Large perovskite grains are obtained by TGA modification but with obvious pinholes, which directly leads to an increased defect density accompanied by a decline in PCE. Encouragingly, the champion PCE achieved for GA-based PSC device (21.32%) is almost 13% or 20% higher than those of the control device or TGA-based device. In addition, GA-modified PSCs exhibit the best stability in light-, thermal-, and humidity-based tests due to the improved film formation.