Photo-stability study of a solution-processed small molecule solar cell system: correlation between molecular conformation and degradation

Solution-processed organic small molecule solar cells (SMSCs) have achieved efficiency over 11%. However, very few studies have focused on their stability under illumination and the origin of the degradation during the so-called burn-in period. Here, we studied the burn-in period of a solution-proce...

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Bibliographic Details
Published in:Science and technology of advanced materials 2018-12, Vol.19 (1), p.194-202
Main Authors: Newman, Michael J., Speller, Emily M., Barbé, Jérémy, Luke, Joel, Li, Meng, Li, Zhe, Wang, Zhao-Kui, Jain, Sagar M., Kim, Ji-Seon, Lee, Harrison Ka Hin, Tsoi, Wing Chung
Format: Article
Language:English
Subjects:
101 Self-assembly / Self-organized materials
209 Solar cell / Photovoltaics
302 Crystallization / Heat treatment / Crystal growth
50 Energy Materials
505 Optical / Molecular spectroscopy
Active control
BTR
Burn-in
Butyric acid
Crystal structure
Crystallinity
Crystallization
Degradation
Focus on Organic and Hybrid Photovoltaics
Molecular conformation
photobleaching
Photoluminescence
Photovoltaic cells
Raman spectroscopy
Rhodamine
Small molecule solar cells
Solar cells
Spectrum analysis
Stability
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Summary:Solution-processed organic small molecule solar cells (SMSCs) have achieved efficiency over 11%. However, very few studies have focused on their stability under illumination and the origin of the degradation during the so-called burn-in period. Here, we studied the burn-in period of a solution-processed SMSC using benzodithiophene terthiophene rhodamine:[6,6]-phenyl C 71 butyric acid methyl ester (BTR:PC 71 BM) with increasing solvent vapour annealing time applied to the active layer, controlling the crystallisation of the BTR phase. We find that the burn-in behaviour is strongly correlated to the crystallinity of BTR. To look at the possible degradation mechanisms, we studied the fresh and photo-aged blend films with grazing incidence X-ray diffraction, UV-vis absorbance, Raman spectroscopy and photoluminescence (PL) spectroscopy. Although the crystallinity of BTR affects the performance drop during the burn-in period, the degradation is found not to originate from the crystallinity changes of the BTR phase, but correlates with changes in molecular conformation - rotation of the thiophene side chains, as resolved by Raman spectroscopy which could be correlated to slight photobleaching and changes in PL spectra.
ISSN:1468-6996
1878-5514
DOI:10.1080/14686996.2018.1433948