Inkjet-Printed Cu(In,Ga)(S,Se)(2) Thin Film Solar Cells Exceeding 15% Power Conversion Efficiency

Cu(In,Ga)(S,Se)(2) (CIGSSe) solar cells are one of the most promising thin film photovoltaics with a record efficiency of 23.6%. However, the biggest drawback to CIGSSe solar cells is their high material cost, partially resulting from relatively rare and expensive indium and gallium. Therefore, improving the utilization of indium and gallium and reducing their wastage can greatly lower the cost of CIGSSe thin film solar cells. Inkjet printing is a facile, cost-effective, and low-waste deposition technology, which is particularly suitable for low-cost and large-area fabrication of CIGSSe solar cells. Herein, a novel and green ionic liquid-assisted ink to fabricate highly efficient CIGSSe solar cells is developed. The material utilization of inkjet printing can be remarkably improved compared to the conventional vacuum-based deposition approach and spin-coating solution approach. The CIGS printable ink is prepared by dissolving copper acetate, indium acetate, gallium nitrate, and thiourea into ethanol with the assistance of n-butylammonium butyrate ionic liquid. Ionic liquid-assisted CIGS ink has a nearly zero wetting angle and a tunable viscosity, which enable to deposit a flat and continuous CIGS thin film by an inkjet printing method. An encouraging power conversion efficiency of 15.22% has been achieved for inkjet-printed CIGSSe solar cells.