Efficient and stable formamidinium-caesium perovskite solar cells and modules from lead acetate-based precursors

Controlling the crystallization process of perovskite thin films to obtain a high-quality material is one of the most challenging aspects for upscaling perovskite solar cell (PSC) technology. The use of non-halide lead sources, such as lead acetate, is a potential solution to this issue due to the fast perovskite crystallization process triggered by the facile removal of acetate during post-annealing. However, to date, lead acetate has been used exclusively as a precursor for the synthesis of methylammonium (MA) or caesium (Cs) based perovskites, which are unstable and less efficient. Here, we expand the lead acetate precursor route to form mixed A-cation perovskites, namely, formamidinium-caesium lead perovskite. High-quality large-area formamidinium-caesium mixed-cation perovskite films were produced by blade-coating a lead acetate-based precursor formulation in an ambient laboratory environment, with the use of NH4+ as a volatile cation to drive off acetate during annealing, leading to formation of PSCs with a power conversion efficiency (PCE) of up to 21.0%. Blade coated mini-modules with an aperture area of 10 cm(2) displayed PCEs of up to 18.8%. The encapsulated PSCs showed excellent thermal stability, with no evidence of efficiency loss after 3300 hours at 65 degrees C.