Efficient defect-passivation and charge-transfer with interfacial organophosphorus ligand modification for enhanced performance of perovskite solar cells

Interfacial engineering is an effective method to improve the performance of perovskite solar cells. Nevertheless, it is still challenging to find a material as interfacial layer with the dual function of defect-passivation and efficient charge-transfer. In this work, organophosphorus ligands, trioctylphosphine oxide (TOPO) and triphenylphosphine oxide (TPPO), were used as passivators through antisolvent process for the interfacial modification. Significantly, the organophosphorus ligands can effectively passivate the defects of perovskite crystals through the formation of Pb-O bond between organophosphorus ligand and undercoordinated Pb2+ ion in perovskite. More interestingly, benzene rings with pi electron in TPPO facilitate the charge transfer between perovskite and hole-transporting layer, achieving the best power conversion efficiency of 18.29% with negligible hysteresis, as well as excellent long-term stability with remaining nearly 85% of the initial efficiency after 2000 h storage under 50% humidity ambient air. In contrast, uncharged octyl alkanes in TOPO hinder the charge transfer and lead to the accumulation of charges at interface although it is a good passivator in light emitting devices for charge confinement. Our findings shed light on the importance of efficient transfer when defect-passivation is employed in solar cell.