Heteroepitaxy with PbSe Nanocrystals Enables Highly Stable Wide-Bandgap Perovskite Solar Cells

The perovskite-based tandem solar cell is one of the promising technological pathways to achieve high efficiency. However, the mixed-halide perovskite top cell is prone to phase segregation under continuous illumination, which leads to rapid degradation of the tandem device's overall power output. To tackle this challenge, ligand-free lead selenide (PbSe) nanocrystals are introduced into the precursor solution to promote the heteroepitaxial growth of mixed-halide perovskite. The incorporation of PbSe results in a high-quality perovskite film with excellent uniformity and low defect density, effectively suppressing halide phase segregation. This improved perovskite thin film enables the fabrication of wide-bandgap (1.68 eV) perovskite Cs_0.05(FA_0.77MA_0.23)_0.95Pb(I_0.77Br_0.23)₃ p-i-n devices, achieving a power conversion efficiency (PCE) of 22.87% and a fill factor (FF) of 84.79%. After 1000 h of maximum power point (MPP) tracking under 1-sun continuous illumination, the perovskite solar cells retain 88% of their initial efficiency. Additionally, by mechanically stacking the semi-transparent perovskite on copper indium gallium selenide (CIGS) solar cells, the 4-terminal tandem cell has demonstrated a PCE of 28.24%.