Electronic Band Engineering via MI3 (M = Sb, Bi) Doping Remarkably Enhances the Air Stability of Perovskite CsSnI3

CsSnI 3 is a representative all-inorganic and less toxic perovskite material. However, extreme structural and chemical instability of perovskite CsSnI 3 makes its optoelectronic applications highly challenging. Upon exposure to air and moisture, it immediately undergoes a phase transition to a thermodynamically more stable, but optoelectronically inactive, one-dimensional polymorph near ambient temperature and ultimately deforms into Cs 2 SnI 6 . To prohibit this undesirable process, perovskite CsSnI 3 has to be stored and treated restrictively in an inert atmosphere and encapsulated hermitically. Here, we demonstrate an unusual strategy to markedly enhance the air stability of perovskite CsSnI 3 . Namely, MI 3 (M = Sb, Bi) doping modifies the electronic band structure of perovskite CsSnI 3 . As a result, it is remarkable that its heat of formation reduces, being lower than that of its c…