Highly efficient and thermally stable Sb₂Se₃solar cells based on a hexagonal CdS buffer layer by environmentally friendly interface optimization

For the first time, a hexagonal phase CdS (H-CdS) film fabricated by thermal evaporation is used as the buffer layer in Sb2Se3 solar cells. It is found that the interfacial recombination of Sb2Se3 solar cells based on a H-CdS film has decreased compared with the cubic CdS (C-CdS) film. Theoretical calculations also confirm that the dangling bond density of C-CdS/Sb2Se3 is 10 times larger than that of the H-CdS/Sb2Se3 interface. The efficiency of Sb2Se3 solar cells has been increased by 80%, which mainly resulted from the better spectral response, especially in the long wavelength (600-1000 nm) region. In addition, the introduction of oxygen at the surface of the H-CdS film can enhance the absorption in the short wavelength range (300-600 nm) and optimize the band structure of H-CdS/Sb2Se3 solar cells. Moreover, it is found that an optimum pre-heating time during Al2O3 deposition results in better carrier transport and collection. Finally, an Sb2Se3 solar cell having a 7.35% efficiency with high depletion width and current density is obtained based on an FTO/hexagonal-CdS/Sb2Se3/Al2O3/Au structure. To our surprise, the efficiency of H-CdS/Sb2Se3 solar cells at 200 °C in this structure can still be kept at above 95% of the original value. We believe that our work can serve as a guide for further development of highly efficient and stable CdS/Sb2Se3 solar cells.