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Photo-stability study of a solution-processed small molecule solar cell system: correlation between molecular conformation and degradation / Michael J. Newman; Emily M. Speller; Jérémy Barbé; Joel Luke; Meng Li; Zhe Li; Zhao-Kui Wang; Sagar Jain; Ji-Seon Kim; Harrison Ka Hin Lee; Wing Chung Tsoi
Science and Technology of Advanced Materials, Volume: 19, Issue: 1, Pages: 194 - 202
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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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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 C71 butyric acid methyl ester (BTR:PC71BM) 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.
Small molecule solar cells, BTR, photobleaching, burn-in, Raman spectroscopy, molecular conformation
College of Engineering