Fabrication of wide band-gap CuGaSe2 solar cells for tandem device applications by sputtering from a ternary target and post selenization treatment

Fabrication of wide band-gap (Eg) CuGaSe2 (CGSe) thin film solar cells with large area uniformity and good reproducibility is difficult, which is crucial for tandem cells. In this work, a method was proposed and investigated to overcome this problem. CGSe solar cells were fabricated by sputtering from a ternary CGSe target and post selenization treatment at different temperatures. After selenization, the CGSe grains grow up gradually, and the copper-poor and selenium-rich CGSe absorbers are obtained successfully. The X-ray diffraction peaks are all corresponded to CGSe phase. As the temperature increases from 530 to 570 °C, the average efficiency increases from 1.57% to 3.11%. When the temperature reaches 590 °C, the efficiency drops to 2.38%. The champion device obtained at 570 °C shows an Eg of 1.66 eV and an efficiency of 3.21%, which indicates the potential for the top cell in tandem solar cells.