DOI: https://doi.org/10.36347/sjpms.2025.v12i08.002

Pages: 346-356

A significant advance in solar energy harvesting and efficient storage can be achieved by developing integrated devices that perform both functions simultaneously. In this study, we present the first successful use of the lead-free double perovskite halide Cs₂NaBiI₆ as both electrode and photoelectrode in lithium-ion photobatteries (PHBATs). The Cs₂NaBiI₆ electrode exhibits outstanding electrochemical performance, delivering an initial specific capacity of 450 mAh g⁻¹ and maintaining 150 mAh g⁻¹ after 90 cycles, with remarkable stability even after 500 cycles. Ex situ X-ray diffraction analysis reveals a two-step lithium storage mechanism: reduction of Bi³⁺ to metallic bismuth (Bi⁰), followed by alloying with lithium to form LiBi and Li₃Bi phases. Operated as a photo-rechargeable battery, the PHBAT achieves a peak light-to-power conversion efficiency of 0.27% under 1 sun illumination—among the highest reported for lithium-ion perovskite photobatteries. Chronoamperometric measurements under alternating dark and light conditions confirm enhanced current generation and sustained capacity under illumination, underscoring the role of photogenerated carriers. Demonstrating practical utility, the device can power a 1.5 V digital stopwatch solely using solar energy. Compared to Cs₃Bi₂I₉-based systems, the Cs₂NaBiI₆ PHBAT offers higher specific capacity, superior rate capability, and enhanced cycling stability. These results position lead-free Cs₂NaBiI₆ as a highly promising, eco-friendly candidate for next-generation photo-rechargeable lithium-ion energy storage, enabling cost-effective, fully integrated solar-powered devices.