The Influence of Fullerene Intercalation on Efficiency and Stability of Polymer Solar Cells
Date Issued
2015
Date
2015
Author(s)
Tsai, Zhan-Yu
Abstract
The power conversion efficiency of polymer bulk heterojunction organic solar cells has exceeded 10 %. However, a key challenge to the organic solar cells is the achievement of power conversion efficiency stability. In this study, we systematically investigated the blends composed of poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT) and three fullerenes, including [6,6]-phenyl C61 butyric acid methyl ester (PC61BM), [6,6]-phenyl C71 butyric acid methyl ester (PC71BM), and indene-C60 bisadduct (ICBA). PBTTT has been shown to have a sufficiently large interval between side chains that can be intercalated by all the three fullerenes, but the degree of intercalation is different, in order of PC61BM ~ PC71BM > ICBA, which results in different optical properties and morphology. Particularly, the intercalation can promote the π-π stacking and enhance the crystallinity of PBTTT. The photovoltaic performance of PBTTT/PC71BM cells fabricated by inverted device structure was studied. We found that the stability of PBTTT/PC71BM cells is much better compared to the common used blend of P3HT/PC61BM. It may be attributed to the stable intermixed phase caused by intercalation that doesn’t tend to phase separate with time. We utilized atomic force microscopy (AFM) to characterize the surface of thin films and found that the surface roughness is very small and nearly unchanged with time. In addition, grazing incidence small-angle X-ray scattering (GISAXS) confirms that the size of PC71BM aggregates in thin films does not significantly change with time. These results suggest that the intercalation can enhance the stability of solar cells due to the stable structure it caused, which provides a design principle for a better performance of polymer-based solar cells.
Subjects
Morphology
Intercalation
Solar cell
Bulk heterojunction
Stability
SDGs
Type
thesis
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