Optimization of Cd²⁺ partial electrolyte treatment on the absorber layer for high-efficiency Cu₂ZnSnSe₄ solar cells

Currently, many researchers are focused on promising new energy technologies such as Cu₂ZnSnS₄-based solar cells to replace fossil fuel sources. Investigations into a variety of methods have been done to analyze the interfacial problems and improve the cell interfacial properties via a variety of methods. In particular, In order to improve the electrical performance of Cu₂ZnSnSe₄ (CZTSe) based solar cells, the Cd partial electrolyte (Cd PE) treatment that is an effective method in CIGS solar cells prior to applying their CdS buffer layer to their absorber layer has been studied. In our study, we investigated the Cd PE treatment time, the Cd PE bath temperature, and the correlation between Cd PE treatment and CdS thickness. The optimum Cd PE absorber treatment was 7 min at 70 °C, with a CdS layer of 35 nm thick deposited cells. This combination increased photo-carrier collection in the short wavelength range and reduced absorber-buffer interface recombination. The efficiency of a 35 nm buffer layer sample without PE treatment was 8.90%. The efficiency of another 35 nm buffer layer sample was 10.38% (Voc: 441 mV, Jsc: 38.15 mA/cm2, and FF: 61.58%) after Cd PE treatment due to the increase of Jsc, FF and Rs despite the deficit of Voc.