Optimization of Stable Quasi-Cubic FAxMA1-xPbI3 Perovskite Structure for Solar Cells with Efficiency beyond 20%

Complex compositional engineering of mixed halides/mixed cations perovskites has recently fostered a rapid progress in perovskite solar cell technology. Here we demonstrate that when 10% of formamidinium (FA(+)) is simply added into methylammonium lead iodide (MAPbI(3)) a highly crystalline and compositionally uniform perovskite is formed, self-organizing into a stable quasi-cubic phase at room temperature. We reached power conversion efficiency of over 20.2%, the highest value reported to date for FA(x)MA(1-x)PbI(3) perovskite.