The field of polymer organic photovoltaics (OPV) has made very impressive improvements over the last 10 years with power conversion efficiencies increasing from 5% to 14%. The design of new polymer donors and non-fullerene (NFA) acceptors have been the driving force for these large improvements. The Reynolds group designs new classes of polymers with minimal changes to explore how these small changes in the polymer can have larger impacts on the device performance, morphology and electronic properties. Understanding how to fine tune a polymer donor can help design optimal structures for future devices. Below are some of the most recent projects in the group.
One Atom Change
In an attempt to better understand the link between molecular design and OPV device performance, we designed a family of three polymers, differing only by one atom (carbon, silicon, or germanium) and confirmed that they are similar in chemical purity, macromolecular structure, and physical attributes. The differences in their device performances originates from the variation in backbone conformation present in the polymer solutions, which then affected the overall morphology and intermolecular packing structures in the solid state. Using a combination of ultra-fast transient absorption spectroscopy and theoretical calculations, we identify that the lower fill factor in P(DTC-TPD) is a result of a lower lying triplet energy that leads to a greater bimolecular charge recombination.1
1. Lo, C.K.; Gautam, B. R.; Selter, P.; Zheng, Z.; Oosterhout, S. D.; Constantinou, I.; Knitsch, R.; Wolfe, R. M. W.; Yi, X.; Brédas, J. L.; So, F.; Toney, M. F.; Coropceanu, V.; Hansen, M. R.; Gundogdu, K.; Reynolds, J. R. Chem. Mater. 2018, 30, 2995-3009.