Efficient FAPbI3 perovskite solar cells using PMACl additives in two-step deposition method

Recently, most of the record-breaking PSCs are used formamidinium lead triiodide (FAPbI3) as the perovskite absorber due to its narrow bandgap. To stabilize the α-phase of FAPbI3, one of the common ways is introducing MAPbBr3 (where MA is methylammonium) into the perovskite layer. However, the MA+ will sacrifice the thermal stability of devices, while the incorporation of Br– will enlarge the optical bandgap and eventually decreased the photocurrent of PSCs. Here, a convenient strategy is presented to sequentially deposit stable FAPbI3 perovskite layer without MA+/ Br– by introducing the two-dimensional (2D) perovskite materials PMACl. It is speculated that the PMACl can form a 2D structure in grain boundaries which plays the role of template for the growth of α-FAPbI3. In addition to tune the phase transition, the PMACl can improve the crystallization and smooth the morphology of perovskite. As a result, the PSCs with PMACl achieve a PCE of 16.19%, while the control device only exhibits a PCE of 10.67%. This novel method avoids introducing the MA+/ Br–, and provides a facile approach for the efficient FAPbI3 perovskite solar cells.