Influence of an SCN- moiety on the electronic properties of γ-CsPb(SCN)xBr3-x and the performance of carbon-based HTL-free γ-CsPb(SCN)xBr3-x perovskite solar cells

A CsPbBr3 film was prepared by the hot-casting method from a mixed CsBr and PbBr2 solution with an orthorhombic-phase (γ) CsPbBr3 perovskite structure. γ-CsPbBr3 film has a yellow color with a bandgap energy of 2.32 eV. The low SCN- dopant level forming CsPb(SCN)xBr3-x (x = 0.0625, 0.125, 0.01875, 0.25 and 0.5) films maintains an orthorhombic CsPb(SCN)xBr3-x structure with a film bandgap of 2.32-2.34 eV. The calculated bandgap of the optimized γ-CsPb(SCN)xBr3-x structures slightly changed with SCN- dopant levels from x = 0 to x = 0.5. A carbon-based hole transport layer (HTL)-free γ-CsPb(SCN)0.25Br2.75 solar cell delivers the highest efficiency of 4.5% under six conditions compared to a carbon-based HTL-free pure γ-CsPbBr3 solar cell with an efficiency of 3.89%. The stability of the carbon-based HTL-free γ-CsPb(SCN)0.25Br2.75 solar cell is better than that of the carbon-based HTL-free pure γ-CsPbBr3 solar cell with efficiency retention of 88.96% and 61.86% of their initial values, respectively, after a 30-day testing period.