Stable hole-free, carbon-based CsPbI3 perovskite solar cells achieving 12.45 %-efficiency at a low temperature with Mn doping and excess CsBr simultaneously

A small amount of MnI2 and excess CsBr were simultaneously added into the CsPbI3 perovskite precursor solution to achieve stable black phase CsPbI3 at a low temperature. Orthogonal experiment method was used to obtain the optimal process parameter by adopting the L9(34) orthogonal table. The four factors were the doping amount of Mn, the rotation speed of spin-coating the perovskite film, the annealing temperature of the perovskite film and the number of the perovskite layer, respectively. According to the results of the range analysis, the optimal parameters were 0.6 at.% Mn, 5000 rpm, 4 layers of perovskite film and 120 °C annealing temperature, respectively. And the highest PCE of the Mn-doped CsPbBrxI3-x perovskite solar cell was 12.45%, and maintained 88% of the initial PCE after 20 days. From the results of XRD, SEM, XPS, PL, TRPL, TPV, TPC and the other measurements, Mn doping could improve the crystalline property, decrease the defect density, increase the value of Goldschmidt's tolerance factor (τt) and decrease the size of cuboctahedral void, so that it improved the performance and stability of the PSCs.