Buried-Interface Engineering Enables Record Flexible Semitransparent Perovskite Solar Cells and 27.7% Flexible Perovskite/Silicon Four-Terminal Tandems

Flexible semitransparent perovskite solar cells (FS-PSCs) are promising for lightweight PV and flexible tandem top cells, yet high efficiency and mechanical stability are hard to achieve simultaneously. Herein, we develop a buried-interface engineering strategy via neopentylammonium iodide (NPAI) modification on SnO2/perovskite together with a low-loss flexible IZO/Cu-grid electrode. NPAI reconstructs the buried interface, improves crystallinity, and suppresses nonradiative recombination. The optimized FS-PSCs achieve a champion efficiency of 21.4% and average 61.3% NIR transmittance (800−1200 nm), featuring outstanding operational stability over 500 h of maximum power point (MPP) tracking and 94.5% efficiency retention after 2000 bending cycles (10 mm radius). By integrating this semitransparent absorber, all-flexible perovskite/silicon four-terminal tandems reach a record 27.7% power conversion efficiency (PCE), setting a benchmark for flexible tandem photovoltaics.