Lead acetate as a superior lead source enables highly efficient and stable all-inorganic lead-tin perovskite solar cells

All-inorganic lead–tin (Pb-Sn) perovskite solar cells (PSCs) offer a promising alternative for the conventional organolead halide hybrid perovskite-based photovoltaic, and lead iodide (PbI2) has been commonly used as the lead source for Pb-Sn PSCs, however it is hard to obtain phase-pure CsPbxSn1-xX3 (X = I, Br) perovskite films with specific composition. Herein, lead acetate (Pb(Ac)2) was applied as an alternative lead source substituting PbI2 along with addition of methylamine iodide (MAI) as a supplementary iodine source, affording homogeneous phase-pure CsPb0.4Sn0.6I2.4Br0.6 perovskite film. Pb(Ac)2 has comparable Pb2+ release rate to that of Sn2+ from SnI2, preventing from inhomogeneous crystallization process. Pb(Ac)2 lead source further helps to suppress the nonradiative recombination, reduce trap states, and improve interfacial charge transport, leading to dramatic PCE enhancement. As a result, the inverted-structure CsPb0.4Sn0.6I2.4Br0.6 PSC device based on Pb(Ac)2 lead source delivers a certified power conversion efficiency (PCE) of 13.88 %, which is the highest value among all-inorganic Pb-Sn PSCs reported up to now. Pb(Ac)2 lead source further benefits simultaneous improvements of the thermal and operational stabilities of PSC devices.