Polar molecules modify perovskite surface to reduce recombination in perovskite solar cells

Thin film solar cells can work efficiently by successful interfacial charge separation/collection. The solution-processed perovskite (CH3NH3PbI3) film carries many trap states on the surface, which is detrimental to the high performance of solar cells. Therefore, it is of great urgency to control the interface in the device. In this study, polar silane molecules with amino end groups are self-assembled at the interface of the perovskite/hole transport materials, which works efficiently for the cells even without enough thermal annealing. It reforms the surface of the insufficiently annealed perovskite film, which leads to a normally performing solar cell without the S-shaped current density–voltage curve. For sufficiently annealed perovskite film, the small amount of PbI2 formed and a Si–O–Si network at the interface passivates the surface traps and acts as an energy barrier to reduce recombination in the perovskite solar cells. With the amino-ended silane modification, the optimized performance of the perovskite solar cell reaches 11.8%, which shows great advantages over the original device with a performance of 8.25% (0.92 Sun, AM1.5).