An all-solid-state photo-rechargeable battery based on CsBiI

Here, we present a new two-electrode photo-rechargeable FTO/TiO 2 /Cs 3 Bi 2 I 9 /Pt/FTO system. The key material is the photoactive lead-free perovskite Cs 3 Bi 2 I 9 , which performs photoelectric conversion and provides energy storage. This study is the first example of a battery system in which charging and discharging are based on bismuth redox chemistry. In the photo-charged state, the fabricated battery has an open-circuit voltage of ∼0.28 V in the dark. With a series-connected pack of these batteries, an LED was lit for tens of seconds in the dark. The mechanism of FTO/TiO 2 /Cs 3 Bi 2 I 9 /Pt/FTO cells is that the illumination provides photoexcited electrons for the reduction of Bi 3+ ions, and then, the reduced Bi is reoxidized to Bi 3+ during the discharge process through an external circuit.