Fabrication of bendable and narrow bandgap Cu(In,Ga)(S,Se)2 for tandem photovoltaics

Abstract Cu(In,Ga)(S,Se)2 absorbers with a bandgap in the near-infrared region are ideal candidates for a bottom cell in multi-junction solar cell architectures. In flexible and lightweight form factors, such devices could help power many applications through integrated solar cells. Here, we show the use of a two-step method to synthesize Cu(In,Ga)(S,Se)2, with a bandgap between 1.00 and 1.13 eV, on bendable ultra-thin glass, with minority carrier lifetimes approaching 100 ns, in a homogenous and repeatable fashion. We also report on conventional and alternative device fabrication methods with very low waste and toxicity footprints. Champion solar cells are fabricated based on absorbers with a graded bandgap between 1.05 and 1.1 eV, and an open circuit voltage approaching 600 mV. Our results show a way for scalable fabrication of all thin-film, flexible tandem solar cells, by means of industrially relevant processing steps in a low cost and sustainable fashion.