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Origin of the Mixing Ratio Dependence of Power Conversion Efficiency in Bulk Heterojunction Organic Solar Cells with Low Donor Concentration

Cited 4 time in Web of Science Cited 4 time in Scopus
Authors
Song, Hyung-Jun; Kim, Jun Young; Lee, Donggu; Song, Jiyun; Ko, Youngjun; Kwak, Jeonghun; Lee, Changhee
Issue Date
2013-12
Publisher
American Scientific Publishers
Citation
Journal of Nanoscience and Nanotechnology Vol.13 No.12, pp. 7982-7987
Keywords
복합학Organic Photovoltaic CellsSmall MoleculeBulk HeterojunctionDonor–Acceptor Mixing Ratio
Abstract
We studied the origin of the improvement in device performance of thermally evaporated bulk heterojunction organic photovoltaic devices (OPVs) with low donor concentration. Samples with three different donor-acceptor mixing ratios, 0:10 (C70-only), 1:9 (low-doped) and 3:7 (high-doped), were fabricated with 1,1-bis-(4-bis(4-methyl-phenyl)-amino-phenyl)-cyclohexane (TAPC):C70. The power conversion efficiencies (PCEs) of these samples were 1.14%, 2.74% and 0.69%, respectively. To determine why the low-doped device showed a high PCE, we measured various properties of the devices in terms of the effective energy band gap, activation energy, charge carrier mobility and recombination loss. We found that the activation energy for charge carrier transport was increased as we increased the TAPC concentration in the blends whereas the hole and electron mobilities became more balanced as the TAPC concentration was increased. Furthermore, the recombination loss parameter alpha (from the light intensity dependence) remained alpha to approximately 0.9 in the low-doped device, but it decreased to alpha to approximately 0.77 in the high-doped device, indicating a large recombination loss as a result of space charge. Therefore, the improved PCE of low-doped OPVs can be attributed to the balance between carrier mobilities with no increase in recombination loss.
ISSN
1533-4880
Language
English
URI
http://hdl.handle.net/10371/90957
DOI
https://doi.org/10.1166/jnn.2013.8155
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College of Engineering/Engineering Practice School (공과대학/대학원)Dept. of Electrical and Computer Engineering (전기·정보공학부)Journal Papers (저널논문_전기·정보공학부)
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