Tuning Surface Wettability of Buffer Layers by Incorporating Polyethylene Glycols for Enhanced Performance of Perovskite Solar Cells

Phenyl-C61-butyric acid methyl ester (PCBM) has been widely researched as a passivate electron transport layer in planar n-i-p-type perovskite solar cells (PSCs). However, due to the terrible wettability of PCBM, the growth of perfect large-area perovskite films on the electron transport layer treated by PCBM is a huge challenge, which limits the commercial application of PSCs. Herein, we incorporate a hydrophilic polymer polyethylene glycol (PEG) into PCBM to ameliorate its wettability. A high-quality perovskite film can be prepared on a 2 × 2 cm substrate. Hydrogen-bonding effects between the PEG-PCBM buffer layer and the perovskite layer can further stabilize the electron transport layer/perovskite interface. Based on the improved electron transport and suppressed carrier recombination, a device with an active area of 1.03 cm² achieves an efficiency of 18.25%. In addition, the first-principles calculations indicate that PEG has stronger adsorption (E_ads = -0.37) toward H₂O than the MAPbI₃ perovskite (E_ads = -0.25), which can prevent water molecules from infiltrating the perovskite. The unsealed device still maintains 90% of the initial efficiency under ambient conditions, with 30-40% relative humidity for 22 days. These outstanding properties are attributed to the unique molecular structure and prominent wettability of PEG.