Effects of Lanthanoid Codoping on Hysteresis Suppression, Long‐Term Stability, and Fill Factor Improvement in Perovskite Solar Cells

In the development of perovskite solar cells (PSCs), ion migration–induced hysteresis, long‐term stability degradation, and reduced fill factor caused by bulk and grain‐boundary defects remain critical challenges. In this study, lanthanoid (Yb/Er, Gd/Nd, Ce/Nd, Gd/Ce, and Yb/Nd) codoped PSCs were fabricated to address these limitations. Lanthanoid elements possess highly localized 4f orbitals and strong Lewis acidity, which enable effective defect passivation and structural stabilization. The Gd and Ce codoped device exhibited enhanced preferential orientation and enlarged grain size, leading to a significant increase in the fill factor to 0.723 due to suppression of bulk defects. The Yb and Nd codoped device effectively suppressed ion migration, reducing the hysteresis index to 0.04 and maintained its conversion efficiency after 112 days of storage under ambient conditions. These results demonstrate that lanthanoid codoping simultaneously mitigates ion migration, defect‐related recombination, and long‐term degradation, providing an effective strategy for improving the performance and stability of PSCs.