Fundamental optical absorption of CsPbI3 and Cs4PbI6

The fundamental optical absorption spectra of CsPbI3 and Cs4PbI6 have been measured for the first time. There are distinct differences in the absorption characteristic between the two compounds: Cs4PbI6 exhibits strong, oscillator-like absorption and a prominent, blue-shifted excitonic peak, compared to the case of CsPbI3. The differences are explainable in terms of whether the Pb2+(I−)6 octahedra are weakly (CsPbI3) or strongly (Cs4PbI6) mutually isolated in the respective compounds.