Bandgap-graded Cu2Sn1-xGexS3 thin film solar cells prepared by sputtering SnGe/Cu targets

Cu2Sn1-xGexS3 (CTGS) thin films were created through sulfurizing SnGe/Cu precursors deposited by the sputtering method. The effects of different sulfurization conditions on the crystallinity, morphology, composition, optical-electrical properties and chemical information of the CTGS thin films have been investigated in detail. The results demonstrate that the CTGS thin films obtained by using sulfurization temperature at 550 degrees C for 20min have the best crystal quality and smooth surface morphology with largest grains and the best optical-electrical properties. Meanwhile, CTGS thin films solar cell with the best performance is found that the CTGS film possesses a graded band gap structure, in which the band gap gradually become larger towards the Mo electrode, and the CdS/CTGS hetero-junction interface shows the "type I '' energy band alignment with a "spike-like" structure. As a result, the obtained bandgap-graded CTGS thin film solar cells with the best power conversion efficiency (PCE) of 3.35 (+/- 0.04) % manifest an open-circuit voltage of 389 (+/- 7.78) mV and a short-circuit current density of 26.98 (+/- 0.54) mA cm(-2). This work demonstrates a promising route to develop high-efficiency Cu(In,Ga)Se-2 or Cu2SnS3-based thin film solar cells.