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

Abstract

In the prior art of CZTSSe solar cells, the traditional cadmium salt (Cd-salt) CdSO 4 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(NO 3 ) 2 , CdCl 2 , and CdAc 2 , on the CZTSSe/CdS heterojunction (HJT) compared to CdSO 4 . CZTSSe/CdS HJT prepared by Cd(NO 3 ) 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(NO 3 ) 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(NO 3 ) 2 possessed the best ability to improve the photovoltaic conversion efficiency (PCE), about 5.7% more than the traditional CdSO 4 salt. After Sn 2+ replaced by Sn 4+ in the precursor solution, the PCE of CZTSSe solar cells using Cd(NO 3 ) 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 MgF 2 antireflective layer).