To improve the interfacial charge transfer that is crucial to the performance of perovskite solar cells, the interface engineering in a device should be rationally designed. Recently, we have reported an interface engineering method to tune the photovoltaic performance of planar heterojunction perovskite solar cells by incorporating MAPbBr_3-xI_x(MA = CH₃NH₃) quantum dots (QDs) between the MAPbI₃ perovskite film and the hole-transporting material (HTM) layer. By adjusting the Br/I ratio, the as-synthesized MAPbBr_3-xI_x QDs show tunable fluorescence and band edge positions. When the valence band (VB) edge of MAPbBr_3-xI_x QDs is located below that of MAPbI3 perovskite, the hole transfer from the MAPbI₃ perovskite film to the HTM layer is hindered and hence the power conversion efficiency decreases. In contrast, when the VB edge of MAPbBr_3-xI_x QDs is located between the VB edge of MAPbI3 perovskite film and the highest occupied molecular orbital (HOMO) of HTM layer, the hole transfer from the MAPbI₃ perovskite film to the HTM layer is well facilitated, resulting in significant improvements of fill factor, short-circuit photocurrent and power conversion efficiency. The photo-generated holes in the perovskite layer are efficiently extracted to the HTM layer with the assistance of MAPbBr_0.9I_2.1 QDs, as revealed by the increased charge carrier lifetime and reduced charge transfer resistance over the interface. A notable increase in power conversion efficiency (PCE) by 29% from 10.34% to 13.32% was thus obtained, suggesting a promising means for interface engineering towards efficient charge carrier extraction and hence high photovoltaic performance.

paper link：http://pubs.acs.org/doi/abs/10.1021/jacs.6b04519