Ag-alloying enables wide-bandgap (1.69 eV) chalcopyrite solar cell with 11.5% efficiency and over 900 mV open circuit voltage from molecular solution

Development of wide-bandgap solar cells is important to expand the application scenarios of photovoltaics, such as building-integrated photovoltaics, tandem solar cells, and indoor photovoltaics. Pure sulfide chalcopyrite Cu(In,Ga)S₂ (CIGS) with high stability is an ideal absorber material for these applications. However, the CIGS are mostly fabricated from high–cost and complicated vacuum-based methods with low-bandgap (< 1.65 eV). Here, we fabricate the wide-bandgap CIGS solar cells from molecular solution through cost-effective and scalable doctor-blading technique. The results show that the performance of intrinsic CIGS solar cells is limited by the low crystallinity of the absorber layer. Incorporating Ag in CIGS by substitution of Cu in the solution significantly improves the absorber crystallinity and reduces the defect concentration. Furthermore, Ag-alloying lowers CIGS energy band without changing bandgap, decreasing conduction band offset at the heterojunction. The greatly reduced charge carrier recombination and charge transfer resistance lead to CIGS solar cell with an efficiency of 11.5% and an open circuit voltage (V_OC) of 904 mV with a bandgap of 1.69 eV, the highest efficiency and lowest V_OC loss of wide-bandgap CIGS solar cell.