Large-Area, Highly Uniform Evaporated Formamidinium Lead Triiodide Thin Films for Solar Cells

Perovskite thin-film solar cells are one of the most promising emerging renewable energy technologies because of their potential for low-cost, large-area fabrication combined with high energy conversion efficiencies. Recently, formamidinium lead triiodide (FAPbI 3 ) and other formamidinium (CH(NH 2 ) 2 ) based perovskites have been explored as interesting alternatives to methylammonium lead triiodide (MAPbI 3 ) because they exhibit better thermal stability. However, at present a major challenge is the scale-up of perovskite solar cells from small test-cells to full solar modules. We show that coevaporation is a scalable method for the deposition of homogeneous FAPbI 3 thin films over large areas. The method allows precise control over film thickness and results in highly uniform, pinhole-free layers. Our films exhibited a high charge-carrier mobility of 26 cm 2 V –1 s –1, excellent optical properties, and a bimolecular recombination constant of 7 × 10 –11 cm 3 s –1 . Solar cells fabricated using these vapor-deposited layers within a regular device architecture produced stabilized power conversion efficiencies of up to 14.2%. Thus, we demonstrate that efficient FAPbI 3 solar cells can be vapor-deposited, which opens up a pathway toward large-area stable perovskite photovoltaics.