Two regioregular narrow band gap conjugated polymers with a D’-A-D-A repeat unit architecture, namely PIFCF and PSFCF, were designed and synthesized. Both polymers contain strictly organized fluorobenzo[c][1,2,5]thiadiazole (FBT) orientations and different solubilizing side chains for solution processing. Compared to the previously reported asymmetric pyridyl-[2,1,3]thiadiazole (PT) based regioregular polymer, namely PIPCP, PIFCF and PSFCF exhibit wider band gaps, tighter π-π stacking, and improved hole mobilities. When incorporated into solar cells with fullerene acceptors, the Eloss = Eg - eVoc values of PIFCF and PSFCF devices are increased compared to solar cells based on PIPCP. Determination of Ect in these solar cells reveals that, relative to PIPCP, PIFCF solar cells lose more energy from Eg - Ect, and PSFCF solar cells lose more energy from both Eg - Ect and Ect - eVoc. The close structural relationship between PIPCP and PIFCF provides an excellent framework to establish molecular features that impact the relationship between Eg and Ect. Theoretical calculations predict that Eloss of PIFCF:PC61BM would be higher than in the case of PIPCP:PC61BM, due to greater Eg - Ect. These findings provide insight into the design of high performance, low voltage loss photovoltaic polymeric materials with desirable optoelectronic properties.
|Original language||English (US)|
|Number of pages||9|
|Journal||J. Mater. Chem. A|
|State||Published - 2017|
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: J. Y. thanks the scholarship for China Scholarship Council (CSC), Collaborative Innovation Center of Suzhou Nano Science & Technology, the Priority Academic Program Development of Jiangsu Higher Education Institutions. Structural characterization efforts were supported by the National Science Foundation (DMR-1411240). Use of the Stanford Synchrotron Radiation Light source, SLAC National Accelerator Laboratory, is supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Contract No. DE-AC02-76SF00515. N.A.R., T.-Q.N., and G.C.B. acknowledge support from the Department of the Navy, Office of Naval Research (Award Nos. N00014-14-1-0580 and N00014-16-1-25200). We would like to thank Kathryn O'Hara for her help with X-ray scattering data collection. Work at KAUST was funded through the KAUST Competitive Research Grant Program. M.K.R. and J.L.B. acknowledge the KAUST IT Research Computing Team and Supercomputing Laboratory for providing outstanding assistance as well as computational and storage resources.