Performance evaluation of two-terminal tandem solar cells using cesium-based lead-free double perovskite top-cell for higher efficiency and better stability

The search for environmentally stable, toxicity-free, higher-efficiency perovskite solar cells has led solar cell research to explore new materials and new cell architectures. It is found that Cesium-based inorganic lead-free perovskites stand to be the best alternative to lead-based perovskites to provide better efficiency and higher environmental stability. In this paper, two lead-free perovskite materials, Cs₂AgBiBr₆ and Cs₂AgBi_0.75Sb_0.25Br₆, have been explored in a tandem cell configuration utilizing the conventional crystalline silicon solar cell for low-energy photon absorption as lower subcell and perovskite absorber for high-energy photon absorption as the upper subcell to provide higher stability and improved efficiency compared to standalone cells using either silicon or perovskite absorbers. Four different upper-subcell configurations have been presented, and the performance of the tandem solar cells has been evaluated using numerical modeling. A filtered solar spectrum has been utilized to assess the lower subcell performance to achieve real-time accuracy. Optimization of the upper and the lower cells has been done to achieve higher efficiency. A power-conversion efficiency as high as 37.49% has been achieved in a two-terminal tandem cell configuration using Cs₂AgBiBr₆ as the perovskite absorber.