Hydrogen halide-free synthesis of organohalides for organometal trihalide perovskite solar cells

We report an environmentally benign and economical approach for the large-scale production of methylammonium halides (MAX, X = I or Br) and formamidinium halides (FAX, X = I or Br) as core materials in perovskite solar cells (PSCs), which have emerged as the most promising sustainable energy source. In contrast to conventional processes that use highly toxic HI and HBr, ion exchange between sodium halide (NaX) and methlyammonium chloride (MACl) or formamidinium chloride (FACl) was found to be highly suitable for mass production. The average reaction yields of the ion-exchange process were comparable to that of the HX synthesis route: 98.8% for MAI, 98.7% for MABr, 98.0% for FAI, and 98.9% for FABr. The purity of the prepared samples was analyzed by various spectroscopic methods. Finally, a perovskite solar cell was fabricated with MAI prepared by ion-exchange reaction. The power conversion efficiency, which was measured to support the industrial feasibility of the method, was found to be similar to that of a device fabricated with commercial MAI.