Photo-rechargeable Li-Ion Batteries with Lead-Free Double-Perovskite Halide Cs₂NaBiI₆

Perovskite halides are promising materials for bifunctional devices that can achieve both photovoltaic energy generation and energy storage. Here, a lead-free all-inorganic double-perovskite halide, 3D Cs₂NaBiI₆, has been investigated as both electrode and photoelectrode active layer in a Li-ion battery. This nontoxic, environmentally friendly material shows impressive lithium storage capacity performance, as compared to previous perovskite photoelectrodes, such as Cs₃Bi₂I_9. Li-ion batteries using this material, in a standard coin cell configuration, achieved a champion first charge specific capacity of 450 mAhg^-1 and 150 mAhg^-1 after 90 cycles, with devices functioning well beyond 500 cycles. Furthermore, bifunctional performance with energy harvesting and energy storage properties was achieved by fabricating photobatteries (PHBATs) in a modified coin cell. PHBATs using Cs₂NaBiI₆ represent the first double perovskite to be used in this application and achieved a "first charge" light conversion efficiency (LCE) of 0.27%, higher than most photoelectrode materials reported to date and with better stability than previously studied bismuth perovskites.