Investigating the Potential of Lead-Free Perovskite/Kesterite Dual Absorber Architectures with Varied Transport Layer Materials for Optimizing Tandem Solar Cell Performance

Sustainable solar energy solutions are made possible by the integration of lead-free perovskite materials with tandem structures, which offer a potential route toward increased stability, less environmental impact, and greater power conversion efficiency (PCE). By absorbing a larger range of the solar spectrum, tandem solar cells have surpassed the ShockleyQueisser efficiency limit and become a significant breakthrough in photovoltaic (PV) technology. This study investigates a new double-absorber tandem solar cell (SC) that uses SCAPS-1D modeling to maximize performance. It consists of a kesteritebased bottom cell (CZTSe) and a lead-free perovskite material called Caesium Titanium Bromide (<tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{Cs}_{2} \text{TiBr}_{6}$</tex>) as the top cell. To identify the ideal device configuration, the study methodically assesses various absorber and transport layer thicknesses, hole transport layers (HTLs), band alignment changes, parasitic resistances and temperature. Quantum efficiency (QE) and J-V characteristics confirm that the proposed double-absorber solar cell efficiently harnesses a broader solar spectrum while maintaining structural stability. Among the simulated configurations, the <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$\text{FTO} / \text{TiO}_{2} / \text{Cs}_{2} \text{TiBr}_{6} / \text{CZTSe}_{2} / \text{Cu}_{2} \mathrm{O} / \text{Ni}$</tex> structure demonstrates the highest photovoltaic performance, achieving a peak PCE of 27.18 %. The device exhibits a shortcircuit current density (Jsc) of <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$42.457 ~\text{mA} / \text{cm}^{2}$</tex>, open-circuit voltage (Voc) of 0.798 V, and fill factor (FF) of 80.26%, highlighting the superior charge transport and minimized recombination losses within the optimized architecture. This study underscores the potential of lead-free perovskite/kesterite tandem SC as a highly efficient and environmentally sustainable alternative to traditional silicon and lead-based perovskite devices. The findings provide valuable insights into optimizing device structure, material selection, and interface engineering to push the boundaries of PV performance.