Highly Sensitive Terahertz Thin Film Total Internal Reflection

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C: Physical Processes in Nanomaterials and Nanostructures

Highly Sensitive Terahertz Thin Film Total Internal Reflection Spectroscopy Reveals in Situ Photoinduced Structural Changes in Methylammonium Lead Halide Perovskites Qiushuo Sun, Xudong Liu, Jie Cao, Rayko Ivanov Stantchev, Yang Zhou, Xuequan Chen, Edward P. J. Parrott, James Lloyd-Hughes, Ni Zhao, and Emma Pickwell-MacPherson J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.8b05695 • Publication Date (Web): 28 Jun 2018 Downloaded from http://pubs.acs.org on June 29, 2018

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The Journal of Physical Chemistry

Figure 1. THz time domain signals of a MAPbI3 perovskite sample and the bare substrate measured in the (a) Transmission system; (b) TF-TIR system. The sample signals are shifted horizontally for clarity. (c) The spectra of the pristine perovskite samples. Dashed lines were measured in transmission while solid lines were measured by TF-TIR. (d) Dove prism setup for THz TF-TIR and schematic of multi-layered system in this setup. Green arrows show the optical paths of the THz light. (e) Normalized and (f) absolute THz amplitudes as a function of sheet conductance calculated by Eqn (2), assuming the reference has a sample conductance of zero. ‘T’, ’R’ and ‘TIR’ correspond to transmission, ordinary reflection and total internal reflection geometry. 307x187mm (150 x 150 DPI)

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Figure 2. THz TF-TIR spectra before (black), after 5 minutes of illumination (red) and after 5 minutes rest in the dark (green) of CYTOP encapsulated (a) MAPbI3, (b) MAPbI2.5Br0.5, (c) MAPbI2Br1 and (d) MAPbBr3. (e) Crystal structure of MAPbI3, showing the ‘octahedral’ and ‘lurching’ modes. 500x263mm (150 x 150 DPI)


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Figure 3. THz spectra from 0.4 THz to 1.6 THz of the CYTOP encapsulated (a) MAPbI3 (b) MAPbI2.5Br0.5 (c) MAPbI2Br1 (d) MAPbBr3 sample varying with exposure times. Representative error bars are given in Figure 3(a): the inset highlights the error bars around the peak. Black color indicates the spectra before the illumination. Markers are measured data, curves are fits using two Lorentzian oscillators. Fitted (e) resonant frequencies, (f) strengths and spectral widths of the ‘octahedral’ peaks. The resonant frequencies of MAPbBr3 in (e) were shifted vertically (minus 0.25 THz) for clarity. 344x190mm (150 x 150 DPI)



Figure 4. (a) visual images (b) XRD patterns (c) THz TF-TIR spectra of the encapsulated MAPbI2Br1 before, after 300 minutes illumination (experimental group), after 300 minutes being kept in dark (control group). The color of the sample turned brown slightly after 300 minutes of light soaking, which could be barely seen by the naked eye. (b) THz TF-TIR spectra of the encapsulated MAPbI2Br1 before, after 300 minutes of illumination and after recovering for 40 minutes in dark. 279x221mm (150 x 150 DPI)


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THz spectra from 0.4 THz to 1.6 THz of the non-encapsulated (a) MAPbI3 (b) MAPbI2.5Br0.5 (c) MAPbI2Br1 (d) MAPbBr3 sample varying with exposure times. Black color indicates the spectra before the illumination. Dots are measured data, curves are the two-oscillator Lorentzian fits. Fitted (e) resonant frequencies, (f) strengths and (g) spectral widths of the ‘octahedral’ peak over 120 minutes of illumination. The resonant frequencies of MAPbBr3 in (e) were shifted vertically (minus 0.25 THz) for clarity. 335x183mm (150 x 150 DPI)



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Highly Sensitive Terahertz Thin Film Total Internal Reflection

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