Multi‐Functional Regulation on Buried Interface for Achieving Efficient Triple‐Cation Perovskite Solar Cells

Abstract Mixed‐cation perovskite solar cells (PSCs) have attracted much attention because of the advantages of suitable bandgap and stability. It is still a challenge to rationally design and modify the perovskite/tin oxide (SnO 2 ) heterogeneous interface for achieving highly efficient and stable PSCs. Herein, a strategy of one‐stone‐for‐three‐birds is proposed to achieve multi‐functional interface regulation via introducing N‐Chlorosuccinimide (NCS) into the solution of SnO 2 : i) C═O functional group in NCS can induces strong binding affinity to uncoordinated defects (oxygen vacancies, free lead ions, etc) at the buried interface and passivate them; ii) incomplete in situ hydrolysis reactions can occur spontaneously and adjust the pH value of the SnO 2 solution to achieve a more matchable energy level; iii) effectively releasing the residual stress of the underlying perovskite. As a result, a champion power conversion efficiency (PCE) of 24.74% is achieved with a device structure of ITO/SnO 2 /Perovskite/Spiro‐OMeTAD/Ag, which is one of the highest values for cesium‐formamidinium‐methylammonium (CsFAMA) triple cation PSCs. Furthermore, the device without encapsulation can sustain 94.6% of its initial PCE after the storage at room temperature and relative humidity (RH) of 20% for 40 days. The research provides a versatile way to manipulate buried interface for achieving efficient and stable PSCs.