Migration-Resistant Phenylethylguanidinium Salts Stabilizing Perovskite Solar Cells

Phenylethylammonium hydrohalide-based passivation layers mitigate trap-assisted recombination in perovskite solar cells by neutralizing defect states and optimizing band bending. However, these layers suffer from thermal instability due to ammonium salt decomposition and bulk migration. To address this, a thermally stable phenylethyl-grafted guanidinium (PEGA+) interfacial layer is introduced. Its delocalized charge distribution, low adsorption energy, and hydrogen-bonding network prevent bulk migration, enhancing stability at elevated temperatures. PEGA+-modified perovskite solar cells (1.55 eV) achieved a power conversion efficiency (PCE) exceeding 26.2%, retaining over 96% of their maximum power after 1100 h and maintaining 89% of their initial performance for 800 h at 85 °C. This strategy is applicable across various device architectures, offering a new molecular design paradigm for long-term interfacial stability in perovskite solar cells.