Photostable Inorganic Perovskite Absorber via Thermal Evaporation for Monolithic Perovskite/Perovskite/Silicon Triple‐Junction Solar Cells

ABSTRACT Monolithic perovskite/perovskite/silicon triple‐junction solar cells have the potential to exceed the efficiency limits of perovskite/silicon dual‐junction solar cells. However, the development of perovskite/perovskite/silicon triple‐junction technology faces several significant hurdles, including the development and integration of a stable high bandgap perovskite absorber into the monolithic structure. Key issues include light‐induced halide segregation in mixed halide high bandgap perovskites and the risk of solvent damage to underlying layers during top‐cell deposition. To overcome these challenges, we developed a high bandgap, inorganic perovskite absorber, CsPbI 2 Br, using thermal evaporation at room temperature, eliminating the need for post‐deposition annealing. The resulting perovskite films exhibited a bandgap of 1.88 eV and demonstrated good photostability without any signs of halide segregation under continuous illumination probed over 3 h. Additionally, thermal evaporation offers a scalable approach for large‐scale production, further enhancing the potential for widespread adoption of this technology. This advancement enabled the incorporation of CsPbI 2 Br perovskite films into a monolithic perovskite/perovskite/silicon triple‐junction device as the top‐cell absorber. Consequently, we developed the first triple‐junction device with an all‐inorganic perovskite top‐cell absorber using the thermal evaporation technique, achieving an efficiency of 21%, with an open‐circuit voltage of 2.83 V over an active area of 1 cm 2 . The device underwent 100 h of fixed voltage measurement near maximum power point under ambient conditions without encapsulation. Remarkably, it not only withstood the measurement but also exhibited an improved efficiency of ~22% afterwards, further demonstrating the stability and reliability of our thermally evaporated CsPbI 2 Br perovskite absorber‐based inorganic solar cell for monolithic triple‐junction perovskite/perovskite/silicon applications.