21.7% Efficiency Achieved in Planar n-i-p Perovskite Solar Cells via Interface Engineering with Water-Soluble 2D TiS2

In planar n-i-p perovskite solar cells (Pero-SCs), interfacial engineering plays a critically important role in charge extraction and transportation, and hence influences the photovoltaic performances. In this study, high performance Pero-SCs were realized by introducing SnO2/2D TiS2 double structures as electron transport layers (ETLs). The highest power conversion efficiency (PCE) reached 21.73% (average PCE is 20.48 +/- 0.50%) with quite small hysteresis. The improvement of performance is mainly attributed to the facilitated charge transportation due to the match of energy levels and decreased electron trap state densities of ETL films. This work provides not only a promising interfacial material, but also a feasible clue to alleviate the trap states of SnO2 in planar n-i-p Pero-SCs.