Highly Efficient Lead-Free Perovskite Solar Cells with Optimized Dual-Absorber Structure

Reducing material toxicity remains a major challenge in the development of high-efficiency perovskite solar cells (PSCs). This study investigates several single and double-absorber PSC structures to identify an optimum structure balancing low toxicity and high-power conversion efficiency (PCE). A novel half-tandem dual-absorber PSC structure consisting of ITO/ SnO 2 / Cs 2 TiBr 6 / Cs 2 AgBiI 6 / P3HT/ NiO x / Au was proposed and analyzed using finite element method (FEM). Additionally, the influence of absorbers thickness, doping and defect densities was examined. Results demonstrate that introducing 400 nm layers of Cs 2 AgBiI 6 and Cs 2 TiBr 6 as main dual absorbers improves the PSC’s performance, increasing short circuit current density and PCE to 31.89 mA/cm 2 , and 32.57 %, respectively due to 19.88 % and 22.48 % escalation in absorption and carrier generation rate compared to conventional MAPbI 3 PSC. Furthermore, optimizing the thickness and defect density of both Cs 2 TiBr 6 upper absorber to 60 nm and 1×10 12 cm -3 , and Cs 2 AgBiI 6 lower absorber to 1200 nm and 1×10 14 cm -3 , respectively, yielded superior performance. The optimal PSC dual absorber structure provided in this study accomplishes short circuit current density of 34.14 mA/cm 2 , open circuit voltage of 1.23 V, and fill factor of 87.82 % with a simulated PCE of 36.87 %, which is theoretically 14.62 % higher than the previously reported PCE value of conventional MAPbI 3 PSC. These findings confirm that the proposed Cs 2 TiBr 6 -Cs 2 AgBiI 6 dual-absorber PSC structure offers a promising non-toxic alternative to the conventional toxic cells with strong potential for future photovoltaic applications.