Efficient and stable all-inorganic perovskite solar cells based on nonstoichiometric CsxPbI2Brx (x > 1) alloys

Here we report a systematic study of all-inorganic perovskite-inspired systems based on CsxPbI2Brx alloys with x ranging from 0.95 to 4. The identified optimal non-stoichiometric composition Cs1.2PbI2Br1.2 delivered the best optoelectronic, structural and photovoltaic characteristics in combination with the improved stability. The elucidated remarkable effect of the Cs4PbI2Br4 impurity phase, serving as a reservoir of CsBr, on the photothermal stability and photovoltaic performance of CsPbI2Br perovskite films offers a new paradigm in the development of more efficient and stable all-inorganic perovskite solar cells.