Influence of sulfurization temperature on photovoltaic properties of Ge alloyed Cu2SnS3 (CTGS) thin film solar cells

•Ge Alloyed Cu2SnS3 (CTGS) thin film solar cells have been successfully fabricated at different annealing temperatures.•Annealing temperature dependence on photovoltaic properties of CTGS thin films was studied.•Ge atoms can be well incorporated to the CTS thin film at annealing temperature of 550 °C.•CTGS thin film solar cell exhibited the highest efficiency of 2.14%.

Ge alloyed Cu2SnS3 (CTGS) thin films were prepared by annealing the sputtered deposited Cu-Ge-Sn precursor films under sulfur atmosphere at different annealing temperatures. The influence of different annealing temperatures on morphological, compositional, crystal structure of CTGS thin films were investigated. It was found that the annealing temperature of 550 °C provides a favorable sulfurization environment to promote grain growth leading to a compact thin film formation. Improved performance is ascribed to high Ge contents as evidenced from X-ray fluorescence (XRF) studies. Well incorporated Ge atoms into CTS thin film can be confirmed by X-ray diffraction (XRD). X-ray photoelectron spectroscopy (XPS) study provides an evidence of existence of Ge atoms where its binding energy located at 25.78 and 26.78 eV, respectively. However, the decreased performance was found at unsuitable annealing temperatures such as 500 °C, 520 °C, 580 °C and 600 °C. Finally, with annealing temperatures of 550 °C, the best power conversion efficiency (PCE) of 2.14% was attained with an open circuit voltage (Voc) of 220 mV, a short circuit current density (Jsc) of 23.74 mA/cm2 and a fill factor (FF) of 41%.