Variable-Temperature Resonance Raman Studies to Probe Interchain Ordering for Semiconducting Conjugated Polymers with Different Chain Curvature
- Authors
- Sutton, Joshua J.; Thanh Luan Nguyen; Woo, Han Young; Gordon, Keith C.
- Issue Date
- 15-4월-2019
- Publisher
- WILEY-V C H VERLAG GMBH
- Keywords
- conducting polymers; long range order; low-frequency Raman; resonance Raman spectroscopy; variable temperature
- Citation
- CHEMISTRY-AN ASIAN JOURNAL, v.14, no.8, pp.1175 - 1183
- Indexed
- SCIE
SCOPUS
- Journal Title
- CHEMISTRY-AN ASIAN JOURNAL
- Volume
- 14
- Number
- 8
- Start Page
- 1175
- End Page
- 1183
- URI
- https://scholar.korea.ac.kr/handle/2021.sw.korea/66013
- DOI
- 10.1002/asia.201801667
- ISSN
- 1861-4728
- Abstract
- The morphology and crystallinity of the polymers used to fabricate bulk heterojuction (BHJ) solar cells significantly influences the efficiency of the cells. We have used variable-temperature (VT) spectroscopy techniques, namely VT emission and VT resonance Raman spectroscopy (VT-RRS), to examine how the backbone linearity of a conducting polymer affects its electronic response to temperature and variations in solution behavior. We have studied two types of donor-acceptor polymers used in BHJ cells with differing backbone structures; they are poly-{5,6-bis(tetradecyloxy)-4-(thiophen-2-yl)benzo[c]-1,2,5-thiadiazole} (PTBT) which has a curved backbone and poly-{5,6-bis(tetradecyloxy)-4-(thieno[3,2-b]-thiophen-2-yl)benzo[c]-1,2,5-thiadiazole} (PTTBT) which has a linear chain structure. Time-dependent density functional theory (TD-DFT) calculations and resonance Raman spectra (RRS) of PTTBT revealed the presence of three electronic transitions, with character that varies between to *, mixed to */charge transfer and pure charge transfer in nature. Emission spectra of PTTBT showed spectral changes at 650 and 710nm with varied temperature (-10 to 60 degrees C). Variable-temperature RRS was measured in resonance with the lowest and highest energy electronic transitions. The changes were interpreted using two-dimensional correlation spectroscopy (2DCOS) analysis. PTTBT showed gradual shifts to lower wavenumbers of modes at around 1425, 1450 and 1500cm(-1). For PTBT larger and more rapid spectral changes are observed at 1440 and 1460cm(-1) consistent with greater variation in the electronic nature upon heating. Further study into the influence of polymer linearity on crystallinity and long range order was carried out using low-frequency Raman (LFR) to examine drop cast films under a variety of different conditions. LFR spectra showed that PTTBT has a band at 73cm(-1). This is observed under a variety of film-forming conditions. PTBT does not show distinct low frequency modes, consistent with its low crystallinity.
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