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Comparison of selenophene and thienothiophene incorporation into pentacyclic lactam-based conjugated polymers for organic solar cells
Article in journal
Renee Kroon, Armantas Melianas, Wenliu Zhuang, Jonas Bergqvist, Amaia Diaz de Zerio Mendaza, Timothy T. Steckler, Liyang Yu, Siobhan J. Bradley, Chiara Musumeci, Desta Gedefaw, Thomas Nann, Aram Amassian, Christian Muller, Olle Inganäs, Mats R. Andersson
Publication Year
Polymer Chemistry, 2015, (6)42, 7402-7409
Link to Source (DOI)
<p>In this work, we compare the effect of incorporating selenophene versus thienothiophene spacers into pentacyclic lactam-based conjugated polymers for organic solar cells. The two cyclic lactam-based copolymers were obtained via a new synthetic method for the lactam moiety. Selenophene incorporation results in a broader and red-shifted optical absorption while retaining a deep highest occupied molecular orbital level, whereas thienothienophene incorporation results in a blue-shifted optical absorption. Additionally, grazing-incidence wide angle X-ray scattering data indicates edge- and face-on solid state order for the selenophene-based polymer as compared to the thienothiophene-based polymer, which orders predominantly edge-on with respect to the substrate. In polymer : PC71BM bulk heterojunction solar cells both materials show a similar open-circuit voltage of similar to 0.80-0.84 V, however the selenophene-based polymer displays a higher fill factor of similar to 0.70 vs. similar to 0.65. This is due to the partial face-on backbone orientation of the selenophene-based polymer, leading to a higher hole mobility, as confirmed by single-carrier diode measurements, and a concomitantly higher fill factor. Combined with improved spectral coverage of the selenophene-based polymer, as confirmed by quantum efficiency experiments, it offers a larger short-circuit current density of similar to 12 mA cm(-2). Despite the relatively low molecular weight of both materials, a very robust power conversion efficiency similar to 7% is achieved for the selenophene-based polymer, while the thienothiophene-based polymer demonstrates only a moderate maximum PCE of similar to 5.5%. Hence, the favorable effects of selenophene incorporation on the photovoltaic performance of pentacyclic lactam-based conjugated polymers are clearly demonstrated.</p>