Highly Efficient and Stable CsPbTh (Th = I, Br, Cl) Perovskite Solar Cells by Combinational Passivation Strategy.

The distorted lead iodide octahedra of all-inorganic perovskite based on triple halide-mixed CsPb(I Br Cl ) framework have made a tremendous breakthrough in its black phase stability and photovoltaic efficiency. However, their performance still suffers from severe ion migration, trap-induced nonradiative recombination, and black phase instability due to lower tolerance factor and high total energy. Here, a combinational passivation strategy to suppress ion migration and reduce traps both on the surface and in the bulk of the CsPhTh perovskite film is developed, resulting in improved power conversion efficiency (PCE) to as high as 19.37%. The involvement of guanidinium (GA) into the CsPhTh perovskite bulk film and glycocyamine (GCA) passivation on the perovskite surface and grain boundary synergistically enlarge the tolerance factor and suppress the trap state density. In addition, the acetate anion as a nucleating agent significantly improves the thermodynamic stability of GA-doped CsPbTh film through the slight distortion of PbI octahedra. The decreased nonradiative recombination loss translates to a high fill factor of 82.1% and open-circuit voltage (V ) of 1.17 V. Furthermore, bare CsPbTh perovskite solar cells without any encapsulation retain 80% of its initial PCE value after being stored for one month under ambient conditions.