Exploring New Cadmium Salts to Enhance the Photovoltaic Conversion Efficiency of Cu₂ZnSn(S,Se)₄ Solar Cells

In the prior art of CZTSSe solar cells, the traditional cadmium salt (Cd-salt) CdSO4 is widely considered as a common raw material for preparing CdS buffer layers. However, in this study, we systematically demonstrated the phase structure and transmission spectra improvement effect of the other three types of Cd-salts, Cd(NO3)(2), CdCl2, and CdAc2, on the CZTSSe/CdS heterojunction (HJT) compared to CdSO4. CZTSSe/CdS HJT prepared by Cd(NO3)(2) showed the strongest CdS phonon characteristic peaks at 295.9 and 597.6 cm(-1), indicating a pure crystal phase. The transmittance of CdS films prepared by Cd(NO3)(2) is 20-35% higher than the other three Cd-salts in the light range of 350-1000 nm, which effectively improved the band gap of the films (2.41 eV) and depressed the photon absorption and scattering. Accordingly, CZTSSe solar cells based on the aforementioned Cd-salts showed that Cd(NO3)(2) possessed the best ability to improve the photovoltaic conversion efficiency (PCE), about 5.7% more than the traditional CdSO4 salt. After Sn2+ replaced by Sn4+ in the precursor solution, the PCE of CZTSSe solar cells using Cd(NO3)(2) exceeded 10% (Total area = 0.21 cm(2), PCE = 10.23%, V-OC = 0.485 V, J(SC) = 31.4 mA/cm(2), FF = 67.1%, without MgF2 antireflective layer).