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Title: Unusual infrared absorption increases in photo-degraded organic films

Degradation is among the most pressing problems facing organic materials, occurring through ingress of moisture and oxygen, and light exposure. We determine the nanoscale pathways underlying degradation by light-soaking organic films in an environmental chamber, and performing infrared spectroscopy, to identify atomic bonding changes. We utilize as a prototype the low band gap PTB7-PCBM blend. Films light-soaked in the presence of oxygen show unusual increased absorption at 1727 cm –1 attributable to increased C=O modes, and a broad increase at 3240 cm –1 attributable to hydroxyl (O–H) groups bonded within the organic matrix. Films exposed to oxygen in the dark, or light-soaked in an inert atmosphere, do not exhibit significant absorption changes, suggesting simultaneous exposure of oxygen and light that creates singlet excited oxygen is the detrimental factor. Our ab initio electronic structure simulations interpret these by oxidation at the α-C site of the alkyl chains in PTB7, with an irreversible rupture of the alkyl chain and formation of new C=O and C–O–H conformations at the α-C. Infrared spectroscopy coupled with ab initio simulation can provide a powerful tool for quantifying photo-structural atomic bonding changes. As a result, understanding nanoscale light-induced structural changes will open avenues to designing more stablemore » organic materials for organic electronics.« less
Authors:
 [1] ; ORCiD logo [1] ;  [2] ;  [1]
  1. Ames Lab. and Iowa State Univ., Ames, IA (United States)
  2. Ames Lab., Ames, IA (United States)
Publication Date:
Report Number(s):
IS-J-9374
Journal ID: ISSN 2040-3364; NANOHL
Grant/Contract Number:
1336134; AC02-05CH11231; AC02-07CH11358
Type:
Accepted Manuscript
Journal Name:
Nanoscale
Additional Journal Information:
Journal Volume: 9; Journal Issue: 25; Journal ID: ISSN 2040-3364
Publisher:
Royal Society of Chemistry
Research Org:
Ames Lab., Ames, IA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
OSTI Identifier:
1371901

Shah, Satvik, Biswas, Rana, Koschny, Thomas, and Dalal, Vikram. Unusual infrared absorption increases in photo-degraded organic films. United States: N. p., Web. doi:10.1039/c7nr01132f.
Shah, Satvik, Biswas, Rana, Koschny, Thomas, & Dalal, Vikram. Unusual infrared absorption increases in photo-degraded organic films. United States. doi:10.1039/c7nr01132f.
Shah, Satvik, Biswas, Rana, Koschny, Thomas, and Dalal, Vikram. 2017. "Unusual infrared absorption increases in photo-degraded organic films". United States. doi:10.1039/c7nr01132f. https://www.osti.gov/servlets/purl/1371901.
@article{osti_1371901,
title = {Unusual infrared absorption increases in photo-degraded organic films},
author = {Shah, Satvik and Biswas, Rana and Koschny, Thomas and Dalal, Vikram},
abstractNote = {Degradation is among the most pressing problems facing organic materials, occurring through ingress of moisture and oxygen, and light exposure. We determine the nanoscale pathways underlying degradation by light-soaking organic films in an environmental chamber, and performing infrared spectroscopy, to identify atomic bonding changes. We utilize as a prototype the low band gap PTB7-PCBM blend. Films light-soaked in the presence of oxygen show unusual increased absorption at 1727 cm–1 attributable to increased C=O modes, and a broad increase at 3240 cm–1 attributable to hydroxyl (O–H) groups bonded within the organic matrix. Films exposed to oxygen in the dark, or light-soaked in an inert atmosphere, do not exhibit significant absorption changes, suggesting simultaneous exposure of oxygen and light that creates singlet excited oxygen is the detrimental factor. Our ab initio electronic structure simulations interpret these by oxidation at the α-C site of the alkyl chains in PTB7, with an irreversible rupture of the alkyl chain and formation of new C=O and C–O–H conformations at the α-C. Infrared spectroscopy coupled with ab initio simulation can provide a powerful tool for quantifying photo-structural atomic bonding changes. As a result, understanding nanoscale light-induced structural changes will open avenues to designing more stable organic materials for organic electronics.},
doi = {10.1039/c7nr01132f},
journal = {Nanoscale},
number = 25,
volume = 9,
place = {United States},
year = {2017},
month = {6}
}

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