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New Insights into the Photodegradation Mechanism of the PTB7-Th Film: Photooxidation of pi-Conjugated Backbone upon Sunlight Illumination

Title
New Insights into the Photodegradation Mechanism of the PTB7-Th Film: Photooxidation of pi-Conjugated Backbone upon Sunlight Illumination
Authors
Kim, SangjunRashid, Md Al MamunurKo, TaewonAhn, KyusangShin, YukyungNah, SangheeKim, Myung HwaKim, BongSooKwak, KyungwonCho, Minhaeng
Ewha Authors
김명화
SCOPUS Author ID
김명화scopus
Issue Date
2020
Journal Title
JOURNAL OF PHYSICAL CHEMISTRY C
ISSN
1932-7447JCR Link

1932-7455JCR Link
Citation
JOURNAL OF PHYSICAL CHEMISTRY C vol. 124, no. 5, pp. 2762 - 2770
Publisher
AMER CHEMICAL SOC
Indexed
SCI; SCIE; SCOPUS WOS scopus
Document Type
Article
Abstract
Understanding the photodegradation mechanism of photoactive materials is critical for enhancing the long-term stability of organic photovoltaic cells (OPVs). However, definitive photodegradation mechanisms have not been reported yet. Here we report the comprehensive understanding of the photodegradation mechanism of the PTB7-Th polymer film. UV/vis absorption and photoluminescence spectra show that the pi-conjugated backbone and the intermolecular pi-pi interactions are simultaneously broken under sunlight in air. Raman spectra reveal that the initial photooxidation begins at the thiophene ring in the benzo[1,2-b;3,3-b]dithiophene (BDT) unit, followed by the ring-opening of the thiophene and the break of the pi-conjugated system. Infrared spectra indicate that -S-C=O and -COOH groups are formed as a result of the photooxidation. On the basis of these observations, we propose that the thiophene ring in the BDT unit reacts with oxygen to generate the BDT-O-2 adduct, which then produces thioester and carboxylic acid. The reaction sites in the BDT unit are consistent with the electrophilic attack positions of oxygen predicted by condensed Fukui functions. Furthermore, the DFT calculated spectrum of the proposed oxidation product agrees well with all the spectroscopic observations. Conclusively, the present work provides an important clue for understanding photodegradation of OPV materials.
DOI
10.1021/acs.jpcc.9b09954
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자연과학대학 > 화학·나노과학전공 > Journal papers
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