Proposal and Design of Graded All‐Inorganic CsPbI 3-x Br x Perovskite Solar Cells for Indoor Applications

All‐inorganic perovskites are promising absorber materials for photovoltaic applications because they generally offer better long‐term stability than organic‐inorganic hybrid perovskites. Among them, CsPbI 3–x Br x has attracted attention because of its thermal stability, tunable bandgap (1.74–1.92 eV), and suitability for both outdoor and indoor photovoltaic applications. Here, we propose and simulate graded‐bandgap CsPbI 3–x Br x PSCs optimized for white‐LED illumination using device simulations. The simulated model was first calibrated against an experimental CsPbI 2 Br/CsPbI 3–x Br x perovskite solar cell (PSC) device in which bandgap grading was shown to broaden the absorption window and increase bulk carrier lifetime. Under warm LED illumination (1000 lux, 2900 K), the optimized bandgap grading of our proposed graded structure raised the indoor power conversion efficiency (PCE) from 31.9% for the best uniform‐bandgap device ( E g = 1.88 eV) to about 36.5%. We further identified a cliff‐type conduction‐band offset (CBO) at the perovskite/ETL junction as a principal voltage‐loss channel and proposed cograding the ETL using composition‐tunable Cd 1-y Zn y S to flatten the CBO at the absorber side while lowering the barrier at the ETL/front contact. Finally, after optimizing the proposed dual‐graded CsPbI 3-x Br x /Cd 1-y Zn y S cell as well as the HTL/absorber band alignment, a PCE above 44.5% was achieved under LED light. These results provide design rules for high‐efficiency all‐inorganic PSCs tailored to indoor energy harvesting.