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Issue 8, 2013
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Improving the long-term stability of PBDTTPD polymer solar cells through material purification aimed at removing organic impurities

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Abstract

While bulk heterojunction (BHJ) solar cells fabricated from high Mn PBDTTPD achieve power conversion efficiencies (PCE) as high as 7.3%, the short-circuit current density (JSC) of these devices can drop by 20% after seven days of storage in the dark and under inert conditions. This degradation is characterized by the appearance of S-shape features in the reverse bias region of current–voltage (JV) curves that increase in amplitude over time. Conversely, BHJ solar cells fabricated from low Mn PBDTTPD do not develop S-shaped JV curves. However, S-shapes identical to those observed in high Mn PBDTTPD solar cells can be induced in low Mn devices through intentional contamination with the TPD monomer. Furthermore, when high Mn PBDTTPD is purified via size exclusion chromatography (SEC) to reduce the content of low molecular weight species, the JSC of polymer devices is significantly more stable over time. After 111 days of storage in the dark under inert conditions, the JV curves do not develop S-shapes and the JSC degrades by only 6%. The S-shape degradation feature, symptomatic of low device lifetimes, appears to be linked to the presence of low molecular weight contaminants, which may be trapped within samples of high Mn polymer that have not been purified by SEC. Although these impurities do not affect initial device PCE, they significantly reduce device lifetime, and solar cell stability is improved by increasing the purity of the polymer materials.

Graphical abstract: Improving the long-term stability of PBDTTPD polymer solar cells through material purification aimed at removing organic impurities

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Supplementary files

Article information


Submitted
19 Apr 2013
Accepted
17 Jun 2013
First published
18 Jun 2013

Energy Environ. Sci., 2013,6, 2529-2537
Article type
Paper

Improving the long-term stability of PBDTTPD polymer solar cells through material purification aimed at removing organic impurities

W. R. Mateker, J. D. Douglas, C. Cabanetos, I. T. Sachs-Quintana, J. A. Bartelt, E. T. Hoke, A. El Labban, P. M. Beaujuge, J. M. J. Fréchet and M. D. McGehee, Energy Environ. Sci., 2013, 6, 2529
DOI: 10.1039/C3EE41328D

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