Design of MAPb(BrxI1−x)3-Based Solar Cells: Compositional Optimization for Thermally Stable and Defect-Tolerant Devices

Mixed halide perovskites can be tuned for bandgap, but they are prone to thermal defect deterioration that is difficult to evaluate throughout the whole stoichiometry range. Here, we investigate the relationship between Br composition, trap density, and temperature. It is observed that asymmetric thermal defect trade-offs provide predictive design principles beyond obvious efficiency trends. We use SCAPS-1D to model MAPb(BrxI1−x)3 solar cells. Simulation parameters include continuous bowing-corrected functions of Br fraction (0 ≤ x ≤ 1), temperature (300–350 K), and trap density (1011–1020 cm−3). Despite a trade-off between short circuit current and open circuit voltage with Br incorporation (power conversion efficiency drops from ~25.5% at x = 0 to ~12% at x = 1), important results reveal non-trivial asymmetries: (i) Br-rich compositions are more sensitive to trap-assisted SRH recombination at Nt > 1018 cm−3 than I-rich absorbers; (ii) the thermal degradation coefficient dVoc/dT is lower for Br-rich systems than for I-rich systems, indicating improved thermal tolerance for Br-rich systems; and (iii) these quantitative design guidelines give predicted assistance for producing mixed halide perovskite devices with higher operational stability.