Solution‐Processed Bifacial Cu(In, Ga)(S, Se)2 Thin‐Film Solar Cells with a Frontside Power Efficiency of 9.73%

Cu(In, Ga)(S, Se) 2 (CIGSSe) solar cell is one of the most promising thin‐film solar cells with a record power conversion efficiency (PCE) of 23.6%. Conventional CIGSSe thin‐film solar cells are usually fabricated on Mo‐coated soda‐lime glass substrate, thereby, the sunlight on the rear side cannot be utilized by the monofacial CIGSSe solar cells owing to the opacity of the Mo electrode. CIGSSe solar cells fabricated on transparent conductive oxide (TCO) electrode enable to fabricate bifacial solar cells, which can generate power on both sides of solar cells, so that bifacial solar cells have a high potential application in building‐integrated photovoltaics. However, the PCEs of CIGSSe solar cells fabricated on TCO substrates are significantly lower than those of ones on Mo substrates. In this article, bifacial CIGSSe solar cells on fluorine‐doped tin oxide (FTO) substrate are fabricated by using an ionic liquid‐assisted solution approach and utilizing a MoO 3 thin film as an interface layer between FTO and CIGSSe absorber layer, yielding a front‐side PCE of 9.73% and a back‐side PCE of 1.77%.