The field of polymer organic photovoltaics (OPV) has made impressive improvements over the last 10 years with power conversion efficiencies increasing from 8% to 18%. 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 published projects in the group.
A key factor for OPV materials implementation into industrial relevant devices is their active layer thickness tolerance as solar cell performances are typically reported with thicknesses on the order of 100–150 nm, but thicker films (ca. 300 nm) are needed for printing and roll-to-roll processing. With this in mind, we designed and synthesized two PM7 isomeric derivatives featuring a chlorinated benzodithiophene and ester functionalized terthiophene moieties for the incorporation into non-fullerene OSCs. The fundamental difference between the two isomeric polymers is the location of the ester side chains where the PM7 D1 esters are located on the outer thiophene units, whereas the esters on PM7 D2 are located on the central thiophene unit. This simple modification produced polymers with similar absorption profiles, electrochemical onsets, charge carrier mobilities when blended with ITIC-4F, and grazing-incidence wide-angle X-ray scattering patterns.
1. You, H.; Jones, A.L.; Ma, T.; Kim, G.; Lee, S.; Lee, J.; Kang, H.; Kim, T.; Reynolds, J.R.; Kim, B.J. Ester-functionalized, wide-bandgap derivatives of PM7 for simultaneous enhancement of photovoltaic performance and mechanical robustness of all-polymer solar cells. J. Mater. Chem. C., 2021, 9, 2775-2783.
2. Jones, A.L.; Ho, C.H.; Riley, P.R.; Angunawela, I.; Ade, H.; So, F.; Reynolds, J.R. Investigating the active layer thickness dependence of non-fullerene organic solar cells based on PM7 derivatives. J. Mater. Chem. C., 2021, 8, 15459-15469.