Multifunctional Additive (L-4-Fluorophenylalanine) for Efficient and Stable Inverted Perovskite Solar Cells

The harmful defects accumulated at surfaces and grain boundaries (GBs) limit the performance and stability of perovskite solar cells (PSCs), which results from the poor crystallization and ion migration. Here, a multifunctional molecular additive L-4-fluorophenylalanine (FPA) is explored for highly efficient and stable inverted PSCs. The multifunction is realized through comprehensive defect passivation, surface hydrophobicity, and crystallization control with the multitude groups, such as the amino and carbonyl groups for passivating the unsaturated lead defects at GBs, and the benzene ring for electron-deficient iodine defects, and the fluorine group for the improvement of crystallization and the inhibition of ions migration. The resulting inverted device shows a champion power conversion efficiency of 21.28% with negligible hysteresis. The unencapsulated FPA-modified devices maintain nearly 90% of the initial performance after high-temperature (85 °C) thermal accelerated aging for 500 h and 85% after aging for 4000 h under ambient conditions, and about 90% of the original efficiency after being maximum power point tracked for 1000 h under continuous illumination. This study provides a multipronged strategy to the future design of PSCs with higher efficiency and enhanced stability.