High‐Quality Subsurface Construction of Perovskite Film for Efficient and Stable Solar Cells

Abstract The subsurface of perovskite (PVK) triggers non‐radiative recombination and initiates film degradation due to the impurities and defects. This study investigates the limitations of the conventional surface post‐treatment and proposes an innovative pre‐treatment strategy to achieve complete impurity elimination and defect passivation of the subsurface. The considerable activity of unannealed PVK films provides a sufficient basis for effective subsurface modification. Following the pre‐treatment, the cadmium ions (Cd ²⁺ ) can occupy the lead (Pb) vacancies or substitute lead ions(Pb ²⁺ ), while the introduced ionic ions (I ^‐ ) are able to fill the ionic (I) vacancies. The stronger ionic bond between Cd ²⁺ and I ⁻ helps prevent the loss of I ^‐ , leading to a reduction of defects in film, inhibiting non‐radiative recombination and ionic migration at the interface. This innovative strategy successfully eliminates impurities and passivates defects, resulting in a perovskite subsurface characterized by high crystallinity, low defect density, and minimal impurity. These enhancements contribute to enhanced open circuit voltage (V _OC )and fill factor (FF), leading to an impressive power conversion efficiency (PCE) of 24.49%. Notably, after 1600 h of aging in ambient air, the cell retained 87% of its initial performance.