Over 10% Efficient Cu2CdSnS4 Solar Cells Fabricated from Optimized Sulfurization

Abstract At present, Kesterite‐based thin‐film solar cells, such as Cu 2 ZnSnS 4 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 Cu 2 CdSnS 4 , 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, Cu 2 CdSnS 4 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 °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, Cu 2 CdSnS 4 thin‐film solar cell prepared under optimized conditions (the ratio of 0.83 and 590 °C) has the minimum reverse saturation current, red shift, and the maximum minority carrier diffusion length. Therefore, an efficiency over 10% Cu 2 CdSnS 4 thin‐film solar cell is reported, which shows the highest efficiency among stannite‐based solar cells to date.