Design of a novel and highly stable lead-free Cs2NaBiI6 double perovskite for photovoltaic application

In recent years, lead-based perovskites have become the most promising photovoltaic materials, showing excellent photoelectronic performance. However, the lead-based perovskites also exhibit instability and significant environmental impact. In this study, we have first reported the synthesis and characterization of a new lead-free double perovskite material, Cs2NaBiI6 (CNBI), and determined its crystal structure and optical properties by various testing methods. CNBI has a low band gap of 1.66eV and exhibits high stability against moisture and oxygen in ambient air. We have also inspected the crystal growth process of CNBI and elucidated its crystal growth mechanism. Solar cell devices fabricated with CNBI as the absorber layer have shown great stability and reproducibility.