Interface Modification Uncovers the Potential Application of SnO2/TiO2 Double Electron Transport Layer in Efficient Cadmium-Free Sb2Se3 Devices

An undesirable p–n heterojunction interface of Sb 2 Se 3 absorber with Cd-free electron transport layer (ETL) is one of the key problems hindering the efficiency improvement of Sb 2 Se 3 solar cell. Herein, a promising SnO 2 /TiO 2 ETL coupled with SbCl 3 treatment is introduced to improve the performance of Sb 2 Se 3 solar cell. The mechanism of SbCl 3 treatment on the crystal orientation of Sb 2 Se 3 thin film and the p–n heterojunction interface of Sb 2 Se 3 solar cell is disclosed combined with different characterization methods. The carrier transport property for Sb 2 Se 3 thin film is enhanced, and the conduction band offset (CBO) of TiO 2 /Sb 2 Se 3 interface is reduced from 0.57 to 0.20 eV by forming Sb 2 O 3 interlayer at TiO 2 /Sb 2 Se 3 interface after SbCl 3 treatment, by which the interface recombination and the open circuit voltage deficit of the device can be effectively decreased, and the interface bonding at TiO 2 /Sb 2 Se 3 interface can be effectively improved. Ultimately, the Cd-free Sb 2 Se 3 solar cell with configuration of ITO/SnO 2 /TiO 2 /Sb 2 Se 3 /Au achieves an efficiency of 5.82%, which is the highest efficiency in vapor transport deposition (VTD)-processed Cd-free Sb 2 Se 3 solar cell at present. This work is expected to fill in the blank of VTD-processed Cd-free Sb 2 Se 3 solar cell and offers a valuable reference for future band alignment of Sb 2 Se 3 solar cell.