Gallium arsenide (GaAs) photovoltaic (PV) cells have been widely investigated due to their merits such as thin-film feasibility, flexibility, and high efficiency. To further increase their performance, a wider bandgap PV structure such as indium gallium phosphide (InGaP) has been integrated in two-terminal (2T) tandem configuration.

However, it increases the overall fabrication cost, complicated tunnel-junction diode connecting subcells are inevitable, and materials are limited by lattice matching. Here, high-efficiency and stable wide-bandgap perovskite PVs having comparable bandgap to InGaP (1.8–1.9 eV) are developed, which can be stable low-cost add-on layers to further enhance the performance of GaAs PVs as tandem configurations by showing an efficiency improvement from 21.68% to 24.27% (2T configuration) and 25.19% (4T configuration).

This approach is also feasible for thin-film GaAs PV, essential to reduce its fabrication cost for commercialization, with performance increasing from 21.85% to 24.32% and superior flexibility (1000 times bending) in a tandem configuration.

This work can be an initial step to reach the objective of improving the usability of GaAs PV technology with enhanced performance for applications for which lightness and flexibility are crucial, without a significant additional cost increase.