Analyzing the synergistic effect of Ag and Ge co-incorporation on Cu2ZnSnSe4 thin-film solar cells

At present, the large number of inherent CuZn anti-site defects and harmful [2CuZn + SnZn] defect clusters in the CZTSe film layer limit the further progress of device efficiency. In this paper, Ag and Ge double cations were introduced into the CZTSe film layer, and (CuAg)2ZnSnGeSe4 (CAZTGSe) films were synthesized successfully by the sol-gel method to cut down the above defects and defect clusters to obtain high-efficiency devices. The influences of double cation substitution on CZTSe by partly replacing Cu with Ag and Sn with Ge were developed. The role of Ag, Ge, and Ag + Ge substitution was researched by X-ray diffraction, scanning electron microscopy, current density-voltage (J-V), and external quantum efficiency measurements. By incorporating 5% Ag and 20% Ge double cations into the CZTSe film, the device demonstrated the highest efficiency of 10.12%. In addition, the open circuit voltage (VOC) of 503.57 mV, the short circuit current density (JSC) of 31.36 mA/cm2, and the fill factor (FF) of 64.1% were obtained.