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

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 (Cd²⁺) can occupy the lead (Pb) vacancies or substitute lead ions(Pb²⁺), while the introduced ionic ions (I^-) are able to fill the ionic (I) vacancies. The stronger ionic bond between Cd²⁺ 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.