(Invited) Intramolecular Exchanging Crystallization for Formamidinium Lead Iodide Perovskite Solar Cells

Abstract

Inorganic-organic hybrid solar cells using perovskite metal-halides such as methylammonium lead iodide (MAPbI3) and formamidinium lead iodide (FAPbI3) have great potential for future photovoltaic systems in terms of high efficiency and low-cost. MAPbI3 had opened the field of perovskite solar cells, but FAPbI3 is recently attracting considerable attention for high efficiency exceeding 20 % and superior durability of the perovskite solar cell. However, FAPbI3 had been limited to utilize as a photovoltaic material due to its polymorph of non-perovskite phase and difficulty to make high quality film in solution process. Recently we reported that perovskite phase of FAPbI3 can be stabilized by compositional engineering of FAPbI3 with incorporation of MAPbBr3. In addition, we showed that intramolecular exchanging process successfully offers a way to make high quality FAPbI3 based perovskite film using dimethyl sulfoxide (DMSO) as a mediator to control crystallization of perovskite. The exchange of FAI with DMSO in pre-deposited PbI2(DMSO) film leads to crystallize into perovskite film with small volume expansion, preferred crystallographic orientation, and large grains, yielding to high power conversion efficiency exceeding 20 %. In this talk, FAPbI3 based perovskite solar cells will be discussed in terms of the compositional engineering and intramolecular exchanging process.