Synergic effects of incorporating black phosphorus for interfacial engineering in perovskite solar cells

Continuous breakthroughs in power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs) have been achieved through advances in interfacial engineering. Black phosphorus (BP), an emerging class of semiconducting materials possessing unique characteristics and good electrical properties, has been applied in various modern optical and electronic devices showing promising functions. In this work, BP nanoflakes prepared by liquid-phase exfoliation are applied at the interface between SnO2 electron transport layer (ETL) and the multi-cation mixed halide perovskite active layer. The temporal stability of perovskite crystallized on BP is substantially improved. The champion device with a PCE of 20.3 % with negligible hysteresis is obtained by incorporating BP nanoflakes. Systematic characterizations reveal that BP nanoflakes synergistically optimize critical parameters at the SnO2/perovskite interface through combined effects of reducing surface roughness for better perovskite crystallization, lowering defect density as well as enhancing carrier transport. Inserting BP nanoflakes between the ETL and perovskite improves the carrier transport efficiency while maintaining high light transmittance to the perovskite absorber layer. These experimental findings demonstrate that interfacial engineering using BP nanoflakes provides a straightforward and effective approach for improving PSC performance.