Interface- and Temperature-Sensitive Linear Electric Field Effects on Exciton Absorption of CH3NH3PbI3 Perovskite Films

The influence of applied electric field (FA) on the absorption spectra of a methylammonium lead tri-iodide (MAPbI3) crystalline film sandwiched between a fluorine-doped tin oxide (FTO) layer and a polymer film of poly(methyl methacrylate) (PMMA) (Sample I) and sandwiched between a compact layer of titanium oxide (cp-TiO2) and a PMMA film (Sample II) has been investigated by first harmonic modulation spectroscopy on various temperatures in the range of 290–60 K. The linear electroabsorption spectra, EA(1f), of the MAPbI3 film in Sample I showed very different behaviors in the temperature range above and below 200 K. EA(1f) spectra show a shape similar to the second derivative of the exciton absorption band having a Gaussian profile, and switching between positive and negative signs is generated at 290 K on alternating polarity of FA. With decreasing temperature, the same tendency of FA polarity-dependent EA(1f) switching was maintained until ∼200 K. At temperatures below 200 K, the inversion of the EA(1f) signal was found with the same field direction of FA, and the signal intensity increased with decreasing temperature. In sample II, the polarity-dependent EA(1f) signal was negligibly small at room temperature but became prominent with decreasing temperature and followed the same trend as that in Sample I observed at temperatures below 200 K, indicating that the substrate on which the MAPbI3 film was coated played a conclusive role as the origin of the polarity-dependent EA(1f) spectra. The second-derivative-like shape of the interface- and temperature-sensitive EA(1f) spectra is interpreted in terms of the polarity-dependent linear Stark shift of the exciton absorption band whose peak position depends on the temperature and substrate on which the MAPbI3 film is coated.