In situ optical absorption spectroscopy of annealing behaviours ofquench-deposited films in the binary system CsI– PbI2

Abstract

We have investigated annealing behaviours of quench-deposited films of the binary CsI–PbI2system by in situ optical absorption spectroscopy. Variousfilms composed of multiple crystalline phases of CsPbI3 and/or Cs4PbI6 as well as ofCsI and/or PbI2are obtained, depending on the mixing ratio of the CsI and PbI2.It is difficult to prepare films purely composed of a single CsPbI3 or Cs4PbI6phase alone. However, it is possible to obtain films where crystallites of either CsPbI3 or Cs4PbI6coexist with the CsI phase. Using such films, we measurethe fundamental optical absorption spectrum of CsPbI3 and Cs4PbI6 for the firsttime. Cs4PbI6exhibits stronger oscillator-like absorption compared to CsPbI3,due to the localized nature of both the Pb 6s and 6p states.