Design and Synthesis of Electron Acceptors with Varying Electron Affinity

Undergraduate #31
Discipline: Chemistry and Chemical Sciences
Subcategory: Chemistry (not Biochemistry)

Caria Evans - University of Georgia
Co-Author(s): Yinlong Du, Theodore Hicks, Junxiang Zhang, and Seth R. Marder School of Chemistry and Biochemistry, Georgia Institute of Technology, 901 Ferst Drive, Atlanta, Georgia 30332

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Polymer solar cells (PSCs) are promising sources for renewable energy, harvesting solar energy into electrical energy. At present, state-of-the-art PSCs have exhibited power conversion efficiencies (PCEs) of up to 10?13%. Highly efficient PSCs typically consist of a polymer electron-donor and a small-molecule electron-acceptor. Presently, fullerene derivatives, such as PC[60]BM, are the most commonly used acceptors due to their efficient charge transporting properties. However, fullerenes suffer from limited absorption, difficult functionalization, and high production cost which may limit the full potential use of PSCs. Non-fullerene acceptors with a range of electron affinities were synthesized using an electron-rich, fused-ring core and electron-withdrawing ar ene end groups. Changing the end group allows for tuning the absorption profile of these materials. These narrow band gap electron-acceptors will be matched with medium-band gap donor material for optimal solar energy absorption. Knoevenagel condensation of IDTT-CHO with 2-(3-oxo-2,3-dihydroinden-1-ylidene)-malononitrile, 1,3-diethyl-2-thioxodihydropyrimidine-4,6(1H,5H)-dione, and ethyl-rhodanine afforded the new acceptors ITIC, TBB and ERh respectively. However, ITIC film displays obviously improved light harvesting properties with higher film absorption coefficient of 2.0 M-1cm-1 at 682 nm relative to that of TCF (1.8 M-1cm-1), suggesting its stronger light harvest ability. The difference in LUMO energy levels of ERh, TBB and ITIC are 0.19, -0.07 and ?0.26 eV, respectively (Figure 2 a), which are similar to those of PC [60]BM. Thus, it appears that manipulating the end groups has a significant effect on ELUMO and is promising when compared to commonly used fullerene-base acceptors. Finally, the reported synthetic methodology provides potentially effective alternatives for acceptor material in polymer solar cells.

Funder Acknowledgement(s): NSF CCHF-CSURP

Faculty Advisor: Seth Marder, seth.marder@chemistry.gatech.edu

Role: I assisted in the design and optimization of compounds for the acceptor material. I purified and characterized the dye as well.