Investigation of CsSn0.5Ge0.5I3-on-Si Tandem Solar Device Utilizing SCAPS Simulation

With the perovskite-on-Si tandem solar technology at the onset of commercialization, it becomes imperative to tackle the toxicity concern of Pb in the perovskite structure. This study utilizes solar cell capacitance simulator (SCAPS) simulation software to investigate a tandem device with the crystalline Si (c-Si; bandgap: 1.12 eV) bottom cell in a mechanically stacked configuration with the stable and nontoxic CsSn _0.5 Ge _0.5 I ₃ (bandgap: 1.5 eV) as the top cell active layer. The device performance has been compared against that of a traditional tandem solar device setup utilizing MAPbI ₃ (bandgap: 1.55 eV) as the top cell active layer. Simulation results reveal power conversion efficiency (PCE) values of standalone CsSn _0.5 Ge _0.5 I ₃ , MAPbI ₃ , and c-Si cells to be 7.45%, 20.01%, and 25.95%, respectively, all in good agreement with published experimental results. The current matching condition between the top perovskite cell and the bottom c-Si cell has been probed through variation of perovskite layer thickness, yielding optimized thickness values for CsSn _0.5 Ge _0.5 I ₃ and MAPbI ₃ to be 365 and 225 nm, respectively. A tandem device with CsSn _0.5 Ge _0.5 I ₃ -on-Si showcases a PCE of 28.53% ( ${V}_{\mathrm{oc}}$ : 1.72 V; ${J}_{\mathrm{sc}}$ : 20.02 mA/cm ² ; and FF: 83.74%) compared with an MAPbI ₃ -on-Si device yielding a PCE of 32.29% ( ${V}_{\mathrm{oc}}$ : 1.88 V; ${J}_{\mathrm{sc}}$ : 19.969 mA/cm ² ; and FF: 85.99%). The results and analyses of this study highlight the feasibility of utilizing nontoxic materials, such as CsSn _0.5 Ge _0.5 I ₃ , to attain high tandem device PCE values.