Effects of Surface Blocking Layer of Sb₂S₃ on Nanocrystalline TiO₂ for CH₃NH₃PbI₃ Perovskite Solar Cells

Sb2S3 layers were inserted at the interface between TiO2 and CH3NH3PbI3 perovskite to create CH3NH3PbI3 solar cells using inorganic hole transporting material (CuSCN). The CH3NH3PbI3 layer was spin-coated by a one-drop method onto the nanocrystalline TiO2 layer. The photoenergy conversion efficiencies were improved with Sb2S3 layers (the best efficiency: 5.24%). During the light exposure test without encapsulation, the CH3NH3PbI3 solar cells without Sb2S3 deteriorated to zero efficiency in 12 h and were completely changed from black to yellow because the perovskite CH3NH3PbI3 was changed to hexagonal PbI2. With Sb2S3, on the other hand, the CH3NH3PbI3 solar cells became stable against light exposure without encapsulation, which did not change the crystal structure or the wavelength edges of absorption and IPCE. Therefore, it was believed that degradation can occur at the interface between TiO2 and CH3NH3PbI3.