Numerical Investigation of High-Performance Bilayer Tin-Based Perovskite Solar Cells with SCAPS-1D

Abstract

Lead-free perovskite solar cells (PSCs) based on Tin halide perovskites are gaining attention as sustainable options to Pb-based counterparts because of their favourable optoelectronic properties. In this research, a bilayer absorber framework comprising CsSnI 3 (narrow bandgap) and CsSnCl 3 (wide bandgap) is numerically investigated using SCAPS-1D. The graded bandgap configuration enables complementary photon absorption, effective charge separation, and suppressed non-radiative recombination deficits. Thickness optimization reveals a peak power conversion efficiency (PCE) of 29.16% at a thickness of 1.5 µm for the absorber, achieving a fill factor (FF) of 84.88%, short-circuit current density (Jsc) of 31.86 mA cm -2 , and open-circuit voltage (Voc) of 1.04 V. The CsSnCl 3 top layer serves as a defect-passivating and moisture-resistant interface, while CsSnI 3 provides strong near-infrared light absorption. This bilayer design offers advantages such as lead-free composition, graded energy-level alignment, and improved stability, though challenges related to Sn 2+ oxidation, chloride ion migration, and lattice mismatch remain. These findings emphasize the possibilities of CsSnI 3 /CsSnCl 3 bilayer absorbers for efficiency at a high level, environmentally benign PSCs and provide guidance for future experimental development of stable, lead-free photovoltaics.