Unifying Absorber Doping and Interface Engineering for Barium-Doped All-Inorganic Perovskite Solar Cells for BIPV Applications

The future of perovskite solar cells (PSCs) is increasingly aligned with real-world applications, especially in semi-transparent building-integrated photovoltaics, tandem configurations, and flexible optoelectronics, where achieving an optimal balance of efficiency, stability, and scalability is critical. This article proposes a dual-optimization strategy that concurrently engineers both the perovskite absorber and hole transport layer (HTL), a rarely explored yet crucial approach. Partial substitution of Pb²⁺ with Ba²⁺ in the bromine-rich, wide-bandgap CsPbIBr₂ absorber (E_g ≈ 2.12 eV) improves crystallinity, grain morphology, and defect passivation, enhancing photostability and enabling spectral tunability for tandem and UV-selective applications. Using numerical simulations, three benchmark HTLs, spiro-OMeTAD, PEDOT:PSS, and P3HT, are evaluated, highlighting how optimal energy alignment and refined hetero-interface engineering enhance charge extraction while reducing interfacial recombination in Ba²⁺-doped CsPbIBr₂-based PSCs. The optimized device (FTO/SnO₂/CsPb(Ba)IBr₂/HTL/Au) achieves a power conversion efficiency of 15.63% by suppressing interface trap density to 1 × 10⁹ cm⁻² at the absorber/HTL junction. The article also explores the impact of absorber and HTL thicknesses, interfacial defect densities, carrier capture cross-sections, density of states, and parasitic resistances on optoelectronic behavior. These results underscore the importance of synergistic absorber-HTL coengineering and parameter tuning for high-efficiency, stable, application-ready all-inorganic PSCs.