Characterizing temperature-dependent optical properties of (MA0.13FA0.87) PbI3 single crystals using spectroscopic ellipsometry

• Published in: Scientific reports Vol. 9; no. 1; pp. 1 - 9
• Main Authors: Chen, Hsiao-Wen, Gulo, Desman Perdamaian, Chao, Yu-Chiang, Liu, Hsiang-Lin
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 03.12.2019; Nature Publishing Group
• Subjects: 639/301; 639/301/119; 639/301/119/995; Coexistence; Crystals; Humanities and Social Sciences; multidisciplinary; Optical properties; Phase transitions; Science; Science (multidisciplinary); Single crystals; Temperature
• ISSN: 2045-2322; 2045-2322
• DOI: 10.1038/s41598-019-54636-7

In this paper, we present spectroscopic ellipsometry measurements of (MA 0.13 FA 0.87 )PbI 3 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 and exciton binding energy of 40 meV. With decreasing temperature, the refractive index increased. The room-temperature thermo-optic coefficients were −1.7 × 10 −4 and −2.5 × 10 −4  K −1 at wavelength of 600 and 1200 nm. The exciton peak position and bandgap energy exhibited a redshift, which was attributed to a reverse ordering of the band structures. Additionally, an anomaly in exciton peak position and bandgap 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. Our results provide a foundation for the technological development of lead halide perovskites-based photonic devices at various temperatures.