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°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)Se2 or Cu2SnS3-based thin film solar cells.