Characterizing temperature-dependent optical properties of (MA0.13FA0.87) PbI3 single crystals using spectroscopic ellipsometry
Hsiao-Wen Chen1*, Desman Perdamaian Gulo2, Yu-Chaing Chao1, Hsiang-Lin Liu1
1Department of Physics, National Taiwan Normal University, Taipei, Taiwan
2Department of Physics, Chung Yuan Christian University, Taoyuan, Taiwan
* Presenter:Hsiao-Wen Chen,
We present spectroscopic ellipsometry measurements of (MA0.13FA0.87) PbI3 single crystals assessed at photon energies of 0.73–6.42 eV and at temperatures between 4.4 and 400 K. At room temperature, the refractive index was dispersed as a function of frequency, which is typical of a semiconductor. The absorption spectrum exhibited several electronic transitions. We estimated a room temperature direct band gap of 1.66 ± 0.02 eV. With decreasing temperature, the refractive index increased with the thermo-optic coefficient of – 1.5 x 10-4 K-1 at a wavelength of 1200 nm. The bandgap energy and exciton peak position exhibited a redshift, which was attributed to a reverse ordering of the band structures. Additionally, an anomaly in exciton peak position and band gap occurred at approximately 100–200 K due to the structural phase transition. This phenomenon was associated with the coexistence of MA/FA-disordered and MA/FA-ordered domains.

Keywords: spectroscopic ellipsometry, halide perovskite, band gap, exciton binding energy