Recent progress in Pb-free stable inorganic double halide perovskites

Although the power conversion efficiency (PCE) of CH 3 NH 3 PbI 3 -based solar cells has achieved 22.1%, which is comparable to commercialized thin-film CdTe and Cu(In,Ga)Se 2 solar cells, the long-term stability is the main obstacle for the commercialization of perovskite solar cells. Recent efforts have been made to explore alternative inorganic perovskites, which were assumed to have better stability than organic-inorganic hybrid CH 3 NH 3 PbI 3 . In this short review, we will keep up with experiments and summarize recent progresses of inorganic double halide perovskite, in particular to Cs 2 AgBiBr 6 , Cs 2 AgInCl 6 , Cs 2 InBiBr 6 and their family members. We will also share our opinions on the promise of such class of materials.