Over 10% Efficient Cu2CdSnS4 Solar Cells Fabricated from Optimized Sulfurization

At present, Kesterite-based thin-film solar cells, such as Cu2ZnSnS4 solar cells, involve serious band-tailed states, which leads to low open-circuit voltage, thereby hindering the further improvement of device performance. In stannite-based materials, such as Cu2CdSnS4, the substitution of Zn with Cd can effectively suppress Cu-Cd-related point defects and defect clusters; thus, the band-tailing state is few, which has attracted considerable research attention. In this work, on the basis of using optimized sulfurization and optimizing ratios (Cu/Cd+Sn) and temperatures, Cu2CdSnS4 thin films can be obtained with good quality and single-phase composition, in which the device prepared at a ratio of 0.83 and 590 degrees C has the highest efficiency. Defect analysis shows that the substitution of Zn with Cd can effectively reduce Cu-Cd-related defects and defect clusters (such as 2Cu(Cd)+Sn-Cd) and also decrease Urbach energy, fluctuations of bandgap, and electrostatic potential compared with kesterite-based devices. In particular, Cu2CdSnS4 thin-film solar cell prepared under optimized conditions (the ratio of 0.83 and 590 degrees C) has the minimum reverse saturation current, red shift, and the maximum minority carrier diffusion length. Therefore, an efficiency over 10% Cu2CdSnS4 thin-film solar cell is reported, which shows the highest efficiency among stannite-based solar cells to date.