Numerical Simulation of 30% Efficient Lead-Free Perovskite CsSnGeI3-Based Solar Cells

A cesium tin–germanium triiodide (CsSnGeI₃) perovskite-based solar cell (PSC) has been reported to achieve a high-power-conversion efficiency (PCE > 7%) and extreme air stability. A thorough understanding of the role of the interfaces in the perovskite solar cell, along with the optimization of different parameters, is still required for further improvement in PCE. In this study, lead-free CsSnGeI₃ PSC has been quantitatively analyzed using a solar cell capacitance simulator (SCAPS–1D). Five electron transport layers (ETL) were comparatively studied, while keeping other layers fixed. The use of SnO₂ as an ETL, which has the best band alignment with the perovskite layer, can increase the power conversion efficiency (PCE) of PSC by up to 30%. The defect density and thickness of the absorber layer has been thoroughly investigated. Results show that the device efficiency is highly governed by the defect density of the absorber layer. All the PSCs with a different ETL exhibit PCE exceeding 20% when the defect density of the absorber layer is in the range of 10¹⁴ cm⁻³–10¹⁶ cm⁻³, and degrade dramatically at higher values. With the optimized structure, the simulation found the highest PCE of CsSnGeI₃-based PSCs to be 30.98%, with an open circuit voltage (V_oc) of 1.22 V, short-circuit current density (J_sc) of 28.18 mA·cm⁻², and fill factor (FF) of 89.52%. Our unprecedented results clearly demonstrate that CsSnGeI₃-based PSC is an excellent candidate to become the most efficient single-junction solar cell technology soon.