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분자 분광학 및 동력학 연구단
분자 분광학 및 동력학 연구단
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New Insights into the Photodegradation Mechanism of the PTB7-Th Film: Photooxidation of pi-Conjugated Backbone upon Sunlight Illumination

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Title
New Insights into the Photodegradation Mechanism of the PTB7-Th Film: Photooxidation of pi-Conjugated Backbone upon Sunlight Illumination
Author(s)
Sangjun Kim; Rashid, Md Al Mamunur; Taewon Ko; Kyusang Ahn; Shin, Yukyung; Nah, Sanghee; Kim, Myung Hwa; BongSoo Kim; Kyungwon Kwak; Minhaeng Cho
Publication Date
2020-02
Journal
JOURNAL OF PHYSICAL CHEMISTRY C, v.124, no.5, pp.2762 - 2770
Publisher
AMER CHEMICAL SOC
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. © 2020 American Chemical Society
URI
https://pr.ibs.re.kr/handle/8788114/7233
ISSN
1932-7447
Appears in Collections:
Center for Molecular Spectroscopy and Dynamics(분자 분광학 및 동력학 연구단) > Journal Papers (저널논문)
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