Large-area perovskite solar cells with Cs(x)FA(1-x)PbI(3-y)Br(y) thin films deposited by a vapor-solid reaction method

Large-area, highly uniform Cs(x)FA(1-x)PbI(3-y)Br(y) mixed cation perovskite films were prepared by a facile vapor-solid reaction method. In this method, CsBr and PbI2 were first deposited via thermal evaporation, and then exposed to FAI/FACl vapor to form the Cs(x)FA(1-x)PbI(3-y)Br(y) perovskite. With the incorporation of CsBr, the crystallinity of the FAPbI(3) perovskite could be significantly improved. Meanwhile, the FACl vapor could accelerate the growth rate of the CsxFA(1-x)PbI(3-y)Br(y) perovskite in the vapor-solid reaction process. By optimizing the content of Cs and the ratio of FACl/FAI, we obtained high quality, pin-hole free Cs(0.24)FA(0.76)PbI(3-y)Br(y) films. Based on these films, the small sized perovskite solar cells (PSCs) reached a champion power conversion efficiency (PCE) of 17.29%. Without encapsulation, the device with the Cs(0.24)FA(0.76)PbI(3-y)Br(y) perovskite showed much better moisture and thermal stability in comparison to that with the pristine FAPbI(3) perovskite. Furthermore, we also fabricated PSC modules with a size of 8 x 8 cm(2) and achieved a PCE of 12.24%, indicating that such a vapor-solid reaction method has a certain superiority in the manufacture of large-scale PSCs.