Solution-Processed Organic Solar Cells with Power Conversion Efficiencies of 2.5% using Benzothiadiazole/Imide-Based Acceptors

Abstract
A new series of electron-deficient molecules based on a central benzothiadiazole moiety flanked with vinylimides has been synthesized via Heck chemistry and used in solution-processed organic photovoltaics (OPV). Two new compounds, 4,7-bis(4-(N-hexyl-phthalimide)vinyl)benzo[c]1,2,5-thiadiazole (PI-BT) and 4,7-bis(4-(N-hexyl-naphthalimide)vinyl)benzo[c]1,2,5-thiadiazole (NI-BT), show significantly different behaviors in bulk heterojunction (BHJ) solar cells using poly(3-hexylthiophene) (P3HT) as the electron donor. Two-dimensional grazing incidence X-ray scattering (2D GIXS) experiments demonstrate that PI-BT shows significant crystallization in spin-coated thin films, whereas NI-BT does not. Density functional theory (DFT) calculations predict that while PI-BT maintains a planar structure in the ground state, steric interactions cause a twist in the NI-BT molecule, likely preventing significant crystallization. In BHJ solar cells with P3HT as donor, PI-BT devices achieved a large open-circuit voltage of 0.96 V and a maximum device power-conversion efficiency of 2.54%, whereas NI-BT containing devices only achieved 0.1% power-conversion efficiency. © 2011 American Chemical Society.

Citation
Bloking JT, Han X, Higgs AT, Kastrop JP, Pandey L, et al. (2011) Solution-Processed Organic Solar Cells with Power Conversion Efficiencies of 2.5% using Benzothiadiazole/Imide-Based Acceptors. Chem Mater 23: 5484–5490. Available: http://dx.doi.org/10.1021/cm203111k.

Acknowledgements
This project was funded by the Center for Advanced Molecular Photovoltaics (CAMP), Award No. KUS-C1-015-21, made by King Abdullah University of Science and Technology (KAUST), and by the Global Climate and Energy Project (GCEP), Award No. 1138721. We also thank Dr. Peng Wei for the TGA measurement.

Publisher
American Chemical Society (ACS)

Journal
Chemistry of Materials

DOI
10.1021/cm203111k

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