Germanium substitution effect on the property and performance of Cu_2ZnSnSe_4 thin films and its solar cell having absorber layer made by sputtering with single metallic target plus selenization

摘要

We report on the germanium substitution effect on the Cu2ZnSnSe4 solar cell performance with absorber layer prepared by sputtering with a single metallic target plus further selenization. We synthesized the Cu2Zn(Sn1-xGex)Se films with the [Ge]/([Ge] + (Sn]) percentages of 0%, 5%, 10%, 15%, and 20% when different x ratios were 0, 0.05, 0.1, 0.15, and 0.2. Defect chemistry was studied by measuring the structural, electrical, and optical properties of CZTGSe as a function of dopant concentration. The enhanced device performance was shown with the increased Ge content to CZTSe. The solar cell was fabricated with a stack structure of Ag/ITO/ ZnO/CdS/CZTGSe/Mo/SLG. The efficiencies of CZTGSe films at the Ge percentages of 0%, 5%, 10%, 15%, and 20% were 1.90, 2.35, 3.32, 4.64, and 4.24%, respectively. The further improvement in conversion efficiency of 7.23% was achieved by incorporating a NaF layer between the Mo bottom electrode and CZTGSe absorber to form a Mo-NaF bilayer.