Simulation of native oxide-passivated CsSn${}_{0.5}$Ge${}_{0.5}$I${}_3$ highly stable lead-free inorganic perovskite solar cell

The search for a lead-free, nontoxic, highly stable perovskite phase could end at the native oxide-passivated composition of CsSn${}_{0.5}$Ge${}_{0.5}$I${}_3$. Mainly its remarkable stability is due to a thin native oxide layer (Sn-doped GeO${}_2$) formation over CsSn${}_{0.5}$Ge${}_{0.5}$I${}_3$, which suppresses the Sn${}^{2+}$ oxidation to Sn${}^{+4}$. Herein, the performance of this mixed Sn-Ge perovskite and the role of native oxide is analyzed. The experimental device with 7% efficiency is numerically replicated, utilizing reasonable device configuration, material parameters, and defect model. The low efficiency of CsSn${}_{0.5}$Ge${}_{0.5}$I${}_3$ is due to high bulk defects. The simulation result shows that Sn oxidation suppressing the native oxide layer imparts stability but does not significantly impact device efficiency. The optimization provides passivated design for absorbers with high bulk defects. Low thickness at high defect density is preferable, and higher thickness at lower defect density is optimal for device design. The final optimized device achieves an efficiency of 21%. The results summarized here can provide a guideline for high-efficiency, lead-free, nontoxic stable perovskite solar cells. (© 2023 Wiley‐VCH GmbH)