All-Perovskite Four-Terminal Spectral Splitting Solar Cells of 30% PCE with FAPbI ₃ Wide-Bandgap Perovskite Fabricated by Nanoparticle Technology

All-perovskite multijunction solar cells are one of the important candidates for future photovoltaic devices with high energy conversion efficiency. In the case of double-junction solar cells, it is crucial to improve the performance of the top cell. In this study, we integrated a highly efficient FAPbI3 perovskite wide-bandgap top cell with Sn–Pb mixed perovskites as a narrow-bandgap (NBG) bottom cell, as a spectral splitting four-terminal system enabling a broader WBG–NBG pairing compared to two-terminal architectures. Using the spectral splitter with a cutoff wavelength of 775 nm, a maximum power conversion efficiency (PCE) of 30.2% was accomplished. These results highlight the strong potential of mechanically stacked double-junction perovskite solar cells for further efficiency improvements.