Front cover

This cover highlights the innovative use of erbium chloride (ErCl₃) in tin‐halide perovskite solar cells, achieving record‐breaking performance. By modulating nucleation and crystallization kinetics, ErCl₃ enhances film quality, mitigates defect formation, and improves both efficiency (14.0%) and stability. This study provides a sustainable path forward for lead‐free perovskites, offering a compelling alternative to lead‐based counterparts.image