Researchers from Japan's Tokyo Institute of Technology, University of Oxford in the UK and Colorado State University in the U.S have shown that α-FAPbI3, a promising solar cell material with a cubic perovskite structure that is metastable at room temperature, can be stabilized by introducing a pseudo-halide ion like thiocyanate (SCN–) into its structure. The recent findings provide new insights into the stabilization of the α-phase via grain boundary and pseudo-halide engineering.
A material with good photophysical properties that has recently gained momentum is α-formamidinium lead iodide or α-FAPbI3 (where FA+ = CH(NH2)2+), a crystalline solid with a cubic perovskite structure. Solar cells made of α-FAPbI3 exhibit a remarkable 25.8% conversion efficiency and an energy gap of 1.48 eV. Unfortunately, α-FAPbI3 is metastable at room temperature and undergoes a phase transition to δ-FAPbI3 when triggered by water or light. The energy gap of δ-FAPbI3 is much larger than the ideal value for solar cell applications, making the preservation of the α-phase crucial for practical purposes. To overcome this problem, the team of researchers, led by Associate Professor Takafumi Yamamoto from Tokyo Institute of Technology (Tokyo Tech), has recently presented a new strategy for stabilizing α-FAPbI3.