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Title: Polaron and Exciton Delocalization in Oligomers of High-Performance Polymer PTB7

Abstract

A key characteristic of organic photovoltaic cells is the efficient charge separation in the active layer. Sufficient delocalization of the positive polaron in organic photovoltaics is considered essential for the effective separation of the opposite charges and the suppression of recombination. Here we use light-induced EPR and ENDOR spectroscopy combined with DFT calculations to determine the electronic structure of the positive polaron in PTB7-type oligomers. Utilizing the superior spectral resolution of high-frequency (130 GHz) D-band EPR, the principal components of the g tensors were determined. Pulsed ENDOR spectroscopy at X-band allowed the measurement of H-1 hyperfine coupling constants. A comparison of g tensors and H-1 hyperfine coupling constants of the PTB7-type oligomers with the high-performance PTB7 polymer revealed a delocalization of the positive polaron in the polymer over about four monomeric units, corresponding to about 45 angstrom in length. Our current study thus not only determines the polaron delocalization length in PTB7 but also validates the approach combining EPR/ENDOR spectroscopy with DFT-calculated magnetic resonance parameters. This is of importance in those cases where oligomers of defined length are not easily obtained. In addition, the delocalization of the neutral triplet exciton was also determined in the oligomers and compared with polymermore » PTB7. The analysis revealed that the neutral triplet exciton is substantially more delocalized than the positive polaron, exceeding 10 monomeric units.« less

Authors:
ORCiD logo [1];  [2];  [2]; ORCiD logo [3];  [2]; ORCiD logo [1]
  1. Argonne National Lab. (ANL), Lemont, IL (United States)
  2. Univ. of Chicago, IL (United States)
  3. Chicago State Univ., IL (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES). Chemical Sciences, Geosciences & Biosciences Division; National Science Foundation (NSF); Illinois Space Grant Consortium; National Institutes of Health (NIH)
OSTI Identifier:
1607374
Grant/Contract Number:  
AC02-06CH11357; DMR-1420709
Resource Type:
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 142; Journal Issue: 3; Journal ID: ISSN 0002-7863
Publisher:
American Chemical Society (ACS)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; ENDOR; PTB7 oligomer; density functional theory; electron paramagnetic eesonance; high-frequency EPR; polaron; triplet exciton

Citation Formats

Niklas, Jens, Zheng, Tianyue, Neshchadin, Andriy, Mardis, Kristy L., Yu, Luping, and Poluektov, Oleg G.. Polaron and Exciton Delocalization in Oligomers of High-Performance Polymer PTB7. United States: N. p., 2019. Web. https://doi.org/10.1021/jacs.9b10859.
Niklas, Jens, Zheng, Tianyue, Neshchadin, Andriy, Mardis, Kristy L., Yu, Luping, & Poluektov, Oleg G.. Polaron and Exciton Delocalization in Oligomers of High-Performance Polymer PTB7. United States. https://doi.org/10.1021/jacs.9b10859
Niklas, Jens, Zheng, Tianyue, Neshchadin, Andriy, Mardis, Kristy L., Yu, Luping, and Poluektov, Oleg G.. Fri . "Polaron and Exciton Delocalization in Oligomers of High-Performance Polymer PTB7". United States. https://doi.org/10.1021/jacs.9b10859. https://www.osti.gov/servlets/purl/1607374.
@article{osti_1607374,
title = {Polaron and Exciton Delocalization in Oligomers of High-Performance Polymer PTB7},
author = {Niklas, Jens and Zheng, Tianyue and Neshchadin, Andriy and Mardis, Kristy L. and Yu, Luping and Poluektov, Oleg G.},
abstractNote = {A key characteristic of organic photovoltaic cells is the efficient charge separation in the active layer. Sufficient delocalization of the positive polaron in organic photovoltaics is considered essential for the effective separation of the opposite charges and the suppression of recombination. Here we use light-induced EPR and ENDOR spectroscopy combined with DFT calculations to determine the electronic structure of the positive polaron in PTB7-type oligomers. Utilizing the superior spectral resolution of high-frequency (130 GHz) D-band EPR, the principal components of the g tensors were determined. Pulsed ENDOR spectroscopy at X-band allowed the measurement of H-1 hyperfine coupling constants. A comparison of g tensors and H-1 hyperfine coupling constants of the PTB7-type oligomers with the high-performance PTB7 polymer revealed a delocalization of the positive polaron in the polymer over about four monomeric units, corresponding to about 45 angstrom in length. Our current study thus not only determines the polaron delocalization length in PTB7 but also validates the approach combining EPR/ENDOR spectroscopy with DFT-calculated magnetic resonance parameters. This is of importance in those cases where oligomers of defined length are not easily obtained. In addition, the delocalization of the neutral triplet exciton was also determined in the oligomers and compared with polymer PTB7. The analysis revealed that the neutral triplet exciton is substantially more delocalized than the positive polaron, exceeding 10 monomeric units.},
doi = {10.1021/jacs.9b10859},
journal = {Journal of the American Chemical Society},
number = 3,
volume = 142,
place = {United States},
year = {2019},
month = {12}
}

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