Exceptional Morphology-Preserving Evolution of Formamidinium Lead Triiodide Perovskite Thin Films via Organic-Cation Displacement

Here we demonstrate a radically different chemical route for the creation of HC(NH2)(2)PbI3 (FAPbI(3)) perovskite thin films. This approach entails a simple exposure of as-synthesized CH3NH3PbI3 (MAPbI(3)) perovskite thin films to HC(=NH)NH2 (formamidine or FA) gas at 150 degrees C, which leads to rapid displacement of the MA cations by FA(+) cations in the perovskite structure. The resultant FAPbI(3) perovskite thin films preserve the microstructural morphology of the original MAPbI(3) thin films exceptionally well. Importantly, the myriad processing innovations that have led to the creation of high quality MAPbI(3) perovskite thin films are directly adaptable to FAPbI(3) through this simple, rapid chemical-conversion route. Accordingly, we show that efficiencies of perovskite solar cells fabricated with FAPbI(3) thin films created using this route can reach similar to 18%.