Incorporating thermal co-evaporation in current-matched all-perovskite triple-junction solar cells

Thermal co-evaporation of halide perovskites is a solution-free, conformal, scalable, and controllable deposition technique with great potential for commercial applications, particularly in multi-junction solar cells. Monolithic triple-junction perovskite solar cells have garnered significant attention because they can achieve very high efficiencies. Nevertheless, challenges arise in fabricating these devices, as they require multiple layers and precise current matching across complex absorber stacks. Here we demonstrate a current-matched monolithic all-perovskite p-i-n triple-junction solar cell enabled by controlled thermal co-evaporation of various absorber layers in the stack. The top and middle subcells were fabricated by developing optimized thermally co-evaporated Cs_0.3FA_0.7Pb(I_0.56Br_0.44)₃ (1.80 eV bandgap) and FAPbI₃ (1.53 eV) perovskites, respectively, while the bottom subcell employed a solution-processed Cs_0.25FA_0.75Pb_0.5Sn_0.5I₃ (1.25 eV) perovskite. By optimising absorber thicknesses and compositions through optical modelling, we achieve excellent current matching between the top (9.6 mA cm^-2), middle (9.3 mA cm^-2), and bottom subcells (9.0 mA cm^-2), achieving an overall efficiency of 15.8%. Optical modelling simulations suggest that current matching and efficiency up to 11.4 mA cm^-2 and 37.6% respectively could be attainable using the latest interlayer materials. This work highlights the potential of scalable vapour-based deposition techniques for advancing multi-junction perovskite-based solar cells, paving the way for future developments in this field.