Effects of Ge Alloying on Device Characteristics of Kesterite-Based CZTSSe Thin Film Solar Cells

The impacts of Ge alloying on crystal growth and device properties of kesterite-based CZTSSe thin film solar cells fabricated by chalcogenization of sputtered stacks in S/Se ambient were investigated. It was found that Ge-alloyed CZTSSe material improved the grain growth, compactness of film texture, and crystallinity of absorber layers as, a consequence of the device efficiencies were enhanced from similar to 3 to 6%. The investigations on optoelectronic characteristics of devices illustrated that the improvements in devices were mainly governed by decrease in diode ideality factor, suppression of crossover effect between white and dark J-V curves, and reduction of defect level in Ge-alloyed CZTSSe solar cell device. These results suggest the possibility to achieve a further improvement in the optoelectronic characteristics of the devices that could be accomplished by optimization of the technological processes with a fine-timing of the Ge content in the layers.