The use of electron-conducting (n-type) polymer semiconductors as the electron acceptor in organic photovoltaics offers many potential advantages over fullerene acceptors. Among these is the facile tunability of the optical absorption band, electronic structure, crystallinity, solubility, and charge transport properties. Compared to the negligible visible and near infrared light harvesting by fullerene acceptors, n-type polymers can contribute to light absorption in the solar cell as much as the donor polymer; an important fundamental consequence of this is that photoinduced hole transfer becomes an important pathway for charge photogeneration as is photoinduced electron transfer. Unfortunately, the performance of all-polymer solar cells is still inferior compared to fullerene-based solar cells. Low photocurrent and lack of approaches to optimize polymer/polymer blend morphology are some of the major factors that limit the performance of all-polymer photovoltaic devices. To overcome these challenges, we have developed a series of new naphthalene diimide-based acceptor copolymers and studied their structure-property-performance relationships.1-5 We investigated the photovoltaic properties of all-polymer bulk heterojunction solar cells composed of each of the new acceptor copolymers and poly(3-hexylthiophene) (P3HT) or a thiazolothiazole-dithienosilole copolymer as the donor. The resulting all-polymer solar cells gave power conversion efficiencies of up to 5 % while providing new insights into material design for high performance fullerene-free all-polymer blend photovoltaic cells.
1. Hwang, Y. J.; Ren, G.; Murari, N. M.; Jenekhe, S. A. Macromolecules 2012, 45, 9056.
2. Earmme, T.; Hwang, Y. J.; Murari, N. M.; Subramaniyan, S.; Jenekhe, S. A. J. Am. Chem. Soc. 2013, 135, 14960.
3. Hwang, Y. J.; Murari, N. M.; Jenekhe, S. A. Polym. Chem. 2013, 4, 3187.
4. Hwang, Y. J.; Earmme, T.; Subramaniyan, S.; Jenekhe, S. A. Chem. Commun. 2014, 50, 10801.
5. Earmme, T.; Hwang, Y. J.; Subramaniyan, S.; Jenekhe, S. A. Adv. Mater. 2014, 26, 6080.