Low-Cost CuIn1−xGaxSe2 Ultra-Thin Hole-Transporting Material Layer for Perovskite/CIGSe Heterojunction Solar Cells

This paper presents a new type of solar cellwith enhanced optical-current characteristics using an ultra-thin CuIn1−xGaxSe2 hole-transporting material (HTM) layer (<400 nm). The HTM layer was between a bi-layer Mo metal-electrode and a CH3NH3PbI3 (MAPbI3) perovskite active absorbing material. It promoted carrier transportand led to an improved device with good ohmic-contacts. The solar cell was prepared as a bi-layer Mo/CuIn1−xGaxSe2/perovskite/C60/Ag multilayer of nano-structures on an FTO (fluorine-doped tin oxide) glass substrate. The ultra-thin CuIn1−xGaxSe2 HTM layers were annealed at various temperatures of 400, 500, and 600 °C. Scanning electron microscopy studies revealed that the nano-crystal grain size of CuIn1−xGaxSe2 increased with the annealing temperature. The solar cell results show an improved optical power conversion efficiency at ~14.2%. The application of the CuIn1−xGaxSe2 layer with the perovskite absorbing material could be used for designing solar cells with a reduced HTM thickness. The CuIn1−xGaxSe2 HTM has been evidenced to maintain a properopen circuit voltage, short-circuit current density and photovoltaic stability.