Charge-Transfer Enhancement by PEI/MXene Buffer Layer for Boosting Performance of Inverted Perovskite Solar Cells

Polyethylenimine (PEI) is a promising material for use as a buffer layer between PCBM and the metal cathode of inverted perovskite solar cells (PSCs). Its amine groups generate oriented molecular dipoles, inducing work function shifts at the interfaces, and thereby improving energy alignment. However, the insulator nature of PEI can lead to high series resistance. In this work, we introduced Ti₃C₂T_x MXene into PEI (PEI/MX) to form a solution-processable buffer layer for high-performance p-i-n devices. A set of complementary electrical and spectroscopic techniques confirmed that MXenes optimize PCBM/PEI/MX/Ag interfaces. The improved interfacial features result in suppressed recombination losses, increased charge carrier lifetime, and enhanced extraction of photogenerated charges. These improvements are reflected in the enhanced photovoltaic parameters, particularly the open-circuit voltage and fill factor. Notably, PEI/MX based PSCs show enhanced PCE achieving 22.0 ± 0.8% (23.1% for champion PSC device) when compared to the pure PEI based device (18.9 ± 0.6%). Hence, the results presented in this work indicate that solution-processable PEI/MX is a promising candidate to substitute conventional cathode buffer layer materials.