A stepwise solvent-annealing strategy for high-efficiency four-terminal Perovskite/Cu(InGa)Se2 tandem solar cells

Perovskite and Cu(InGa)Se 2 (CIGS) tandem solar cells are emerging as an exciting prospect to achieve high-performance, cost effective, and lightweight all-thin-film photovoltaics, wherein perovskite solar cells (PSCs) fabricated using high-quality wide-bandgap perovskite films are critical to realize the high-efficiency PSC/CIGS tandem solar cells. Herein, a stepwise dimethyl sulfoxide (DMSO) solvent-annealing strategy is proposed to fabricate wide-bandgap (1.68 eV) Cs 0.15 FA 0.65 MA 0.2 PbI 2.4 Br 0.6 films via stepwise heating recipe, that is annealed at 100 °C firstly and then 80 °C. This modified solvent-annealing method makes for the Cs 0.15 FA 0.65 MA 0.2 PbI 2.4 B r0.6 films with full coverage, large grains, improved crystallinity, and free of impurities. Opaque PSCs with the desired Cs 0.15 FA 0.65 MA 0.2 PbI 2.4 B r0.6 films exhibit a champion power conversion efficiency (PCE) of 21.66 % and excellent stability. Furthermore, using an optimized IZO transparent electrode, the semitransparent PSCs with an impressive PCE of 21.26 % and a high bifaciality factor of 92.2 % are fabricated. These PSCs can further enable the four-terminal (4-T) PSC/CIGS tandem solar cells with a summed PCE of 29.36 %, surpassing of most the similar tandem solar cells reported earlier.