Enhanced Thermal and Photostability of Perovskite Solar Cells by a Multifunctional Eu (III) Trifluoromethanesulfonate Additive

Abstract Perovskite solar cells (PSCs) have witnessed a meteoric rise in device performance. However, maintaining photostability, particularly under thermal stress, remains a challenge due to defect formation in the perovskite layer. This study introduces europium (III) trifluoromethanesulfonate [Eu(OTF) 3 ] as a multifunctional additive in two‐step processed perovskite films, significantly improving the performance and high‐temperature photostability of n‐i‐p PSCs. Density function theory (DFT) calculations reveal that the OTF − anion strongly coordinates with Pb 2+ , effectively inhibiting iodine vacancy defect formation. The addition of Eu(OTF) 3 promotes perovskite grain growth to ≈2 µm and enhances film crystallinity. PSCs with a structure of ITO/SnO 2 /perovskite/PDCBT/NiO x /Au achieve a champion power conversion efficiency (PCE) of 23.8%. Under 85 ± 5 °C and 1 sun illumination at an open circuit in ambient air, the PSCs with Eu(OTF) 3 retain 82% of their initial PCE after aging for 1500 h.