Defect State Dynamics in Lead-Free Perovskite Solar Cells for Enhanced Efficiency

Perovskite photovoltaics have emerged as highly promising candidates for next-generation solar cells, achieving impressive power conversion efficiencies surpassing 22%, rivaling traditional silicon solar cells. Their advantages include lower manufacturing costs, tunable bandgaps, and potential for flexible, lightweight designs. However, the widespread use of lead (Pb) in perovskite absorbers raises significant environmental and health concerns. As a solution, researchers are exploring tin (Sn) as a non-toxic alternative due to its comparable electronic configuration, which may enable it to substitute lead without substantially compromising efficiency. In this study, SCAPS-1D software was employed to simulate lead-free tin-based perovskite solar cells, with a focus on analyzing how varying interface defect densities affect cell performance. Key cell parameters examined included the doping concentration of the perovskite absorption layer and the defect density within the perovskite bulk. Defect density is critical as it creates recombination centers that impede charge transport and decrease device efficiency. Findings from this simulation show that reducing defect density in the perovskite absorption layer notably improves overall cell performance, enhancing charge carrier mobility and reducing recombination losses. To further investigate interface effects, two specific interfaces were introduced: the TiO₂/perovskite interface, which serves as an electron transport layer, and the perovskite/hole transport material (HTM) interface. Analysis revealed that the TiO₂/perovskite interface plays a more substantial role in device performance, primarily due to its influence on carrier density and recombination rates, which are higher at this interface and critical in determining cell efficiency. Optimization of these parameters enabled the simulation of a device reaching a maximum efficiency of 24.63%. This research highlights the importance of interface engineering and defect management in tin-based, lead-free perovskite solar cells, demonstrating a feasible pathway toward environmentally sustainable, high-efficiency photovoltaics.