Improvement of Performance of Cu2ZnSn(S, Se)4 Solar Cells by Low-Temperature Annealing of B-Doped CdS

It is known that high carrier recombination at the p–n junction interface and low carrier separation ability (CSA) are two main problems resulting in low power conversion efficiency (PCE) of the Cu 2 ZnSn(S,Se) 4 (CZTSSe) solar cell. To resolve these problems, one CZTSSe solar cell is prepared through substituting B-doped CdS for CdS in a solar cell with the conventional structure of Ag/ITO/ZnO/CdS/CZTSSe/Mo/SLG and annealing B-doped CdS/CZTSSe/Mo/SLG prior to deposition of ZnO, ITO, and Ag electrode. By optimizing the B doping content in the CdS and annealing temperature and time of the B-doped CdS/CZTSSe, lattice mismatch between CdS and CZTSSe is decreased and width of depletion region is increased, leading to reduction in interfacial recombination, enhancement in CSA and intensity of incident light passing through the B-doped CdS, and so increase in PCE from 7.89% of CZTSSe solar cell using CdS as buffer layer to 10.62%. A mechanism of the increment of the PCE induced by B doping and annealing is suggested. This work proposes a method of increasing PCE of CZTSSe solar cell and advances a deeper understanding of the mechanisms behind various parameters in CZTSSe solar cells through theoretical analysis and calculations.