Efficient and Stable p-i-n Perovskite Solar Cells Enabled by In Situ Functional Group Conversion.

Chemical additives play a critical role in the crystallization kinetics and film morphology of perovskite solar cells (pero-SCs), thus affecting the device performance and stability. Especially, carboxylic acids and their congeners with a -COOH group can effectively serve as ligands to fortify the structural integrity and mitigate the risk of lead efflux. However, direct addition of -COOH into the precursor solution could retard the crystallization kinetics of the perovskite during film formation due to the strong coordination. Here, we present a novel approach of in situ functional group conversion using Bis(2,5-dioxopyrrolidin-1-yl) 4,7,10,13-tetraoxahexadecanedioate (Bis-PEG4-NHS ester) as an additive in the antisolvent, which underwent a functional group transformation from -COOR to -COOH during the annealing process through a hydrolysis reaction of Bis-PEG4-NHS ester. The corresponding hydrolysates exhibit enhanced interactions with PbI ₂ and FAI, contributing to the structural integrity and the defect passivation. Our findings offer valuable insights into the chemical interactions within the crystal growth process, achieving the p-i-n pero-SC device with an efficiency of 25.79% (certified as 25.47%) and notable long-term stability.