Efficient and Stable Perovskite Solar Cells Achieved by Using Bifunctional Interfacial Materials to Modify SnO₂ and MAPbI_3–xCl_x Simultaneously

As an effective electron transport layer, tin oxide (SnO 2 ) has attracted much attention owing to its charge mobility and chemical stability, but it still suffers from high trap at the SnO 2 /perovskite interface. Herein, a simple interface treatment strategy of diethylenetriaminepentakis (methylphosphonic acid) (DETAPMP) to effectively passivate the SnO 2 /MAPbI 3– x Cl x interface is reported. Under the optimal DETAPMP concentration, the average power conversion efficiency (PCE) of MAPbI 3– x Cl x solar cells is improved from 17.27 to 19.41% and the champion device shows a PCE of 20.02%. In the (FAPbI 3 ) 0.95 (MAPbBr 3 ) 0.05 system, the average PCE can be improved from 20.08 to 20.95% and the champion device shows a PCE of 21.65%. Such an enhancement is mainly attributed to two factors: (1) the phosphate group in DETAPMP reacts with SnO to passivate SnO 2 defects and (2) the ammonium group in DETAPMP is expected to balance the PbI 3 – charge and passivate PbI 3 – defects, thus achieving lower charge recombination and better carrier transport. In addition, due to the hydrophobicity of DETAPMP and the reduced grain boundaries in the perovskite film, the long-term stability of the perovskite with DETAPMP-modified SnO 2 is improved under the ambient conditions with 20–30% humidity.