SCAPS-1D design and performance optimization of lead-free bilayer perovskite solar cells with Sr3SbI3/Mg3AsBr3 absorbers and a SrCu2O2 hole-transport layer

Abstract

To improve the photovoltaic performance of Pb-free A$_{3}$BX$_{3}$ halide-perovskite solar cells, four planar device architectures were designed and optimized using SCAPS-1D with Sr$_{3}$SbI$_{3}$ and Mg$_{3}$AsBr$_{3}$ as absorber materials. Different hole-transport-layer materials were further evaluated, and SrCu$_{2}$O$_{2}$ was identified as the most favorable HTL owing to its improved band alignment and carrier-extraction capability. Under the adopted simulation conditions, the single-absorber devices FTO/CdS/Sr$_{3}$SbI$_{3}$/Au and FTO/CdS/Mg$_{3}$AsBr$_{3}$/Au achieve simulated power-conversion efficiency of 24.03\% and 26.10\%, respectively, at an absorber thickness of 1.0~$\mu$m. Constructing the bilayer absorber FTO/CdS/Sr$_{3}$SbI$_{3}$/Mg$_{3}$AsBr$_{3}$/Au further increases the simulated PCE to 30.11\% with a fill factor of 88.07\%. After introducing the SrCu$_{2}$O$_{2}$ HTL and optimizing the absorber thickness, doping concentration, and defect density, the FTO/CdS/Sr$_{3}$SbI$_{3}$/Mg$_{3}$AsBr$_{3}$/SrCu$_{2}$O$_{2}$/Au device reaches a simulated PCE of 34.30\% with an FF of 88.84\%. The improved performance is mainly attributed to favorable interfacial band alignment, enhanced hole extraction, and suppressed recombination in the optimized bilayer structure. A complementary realistic-parameter case study, in which bulk and interface defect densities together with parasitic resistances are simultaneously raised to values typical of fabricated thin-film PSCs, projects an experimentally plausible PCE of approximately 24.06\%, so the 34.30\% value should be read as the upper bound of a defect-aware design envelope. These SCAPS-1D results therefore define quantitative parameter targets -- in particular, an absorber bulk defect density below $\sim10^{15}$~cm$^{-3}$ and interface trap densities below $\sim10^{11}$~cm$^{-2}$ -- to guide the future experimental realization of Pb-free A$_{3}$BX$_{3}$ bilayer perovskite solar cells.