High‐Efficiency Fabry‐Pérot‐Resonance‐Based Color‐Tunable Bifacial Perovskite Solar Cells for Building Integrated Photovoltaics

Abstract Perovskite solar cells (PSCs) are promising for building‐integrated photovoltaics (BIPV) owing to their superior low‐light response and tunable bandgap. However, the implementation of perovskite‐based BIPV still faces critical challenges, primarily due to the inherent trade‐off between achieving color tunability via bandgap engineering and maintaining high power conversion efficiency (PCE), as well as ensuring sufficient operational stability. Here, rear‐side color vibrancy of bifacial perovskite solar cells (BPSCs) is enhanced by introducing a low‐loss ultrathin metal (LLUM) layer at the high‐loss SnO₂/indium zinc oxide (IZO) interface under the guidance of Fabry‐Pérot (F‐P) resonance, achieving 60% coverage of sRGB color gamut for 1.52 eV BPSCs. Furthermore, the incorporation of 4‐methylphenethylammonium chloride (4M‐P) and an in‐situ substrate‐heated‐crystallization strategy enhances carrier diffusion lengths, allowing LLUM‐based BPSCs with a 900‐nm‐thick absorber to achieve a PCE of 23.7% under front illumination. Under albedo conditions of 0.1 and 0.2 sun irradiation intensity, the bifacial PCEs are elevated to 24.9% and 27.4%, respectively. The replacement of metal electrodes with IZO counterparts effectively suppresses metal ion diffusion, enabling BPSC devices to retain 87% of their initial efficiency after 1000 h of thermal aging at 85 °C. These results demonstrate the potential of LLUM‐based BPSCs for efficient, color‐tunable, and stable BIPV.