Synthesis and Study of Supersized Heteroaromatic Small Molecules for Organic Photovoltaics

Abstract

Organic photovoltaics (OPVs) are promising alternatives to conventional inorganic solar cells because of their potential for low cost (low-energy) fabrication, and suitability for lightweight, flexible devices. Polycyclic aromatic hydrocarbons (PAHs) are utilized as active ingredients in OPVs because they can be strongly absorbing, chemically stable, and have properties that are highly tunable through organic synthesis. In particular, contorted hexabenzocoronene (cHBC) is shape-complementary with commonly used fullerene electron acceptors, but is limited by poor absorption overlap with the solar spectrum. Replacing benzene rings on cHBC with heterocyclic moieties, such as benzofuran, results in a bathochromic shift that enables improved visible light absorption. Despite these improvements, heteroatom-containing cHBC derivatives do not absorb broadly between 400 - 500 nm, instead exhibiting more local absorption around 400 nm and 500 nm. This thesis reports the synthesis and characterization of contorted tetrabenzofuranyltetrabenzocircumbiphenyl (cTBFTBCB), a novel heteroaromatic derivative of contorted octabenzocircumbiphenyl (cOBCB) that incorporates benzofuran moieties, and the device properties of solar cells comprising this material. The parent compound, cOBCB, shows strong visible absorption between 400 - 500 nm and has been used in solar cells that exhibit power conversion efficiencies of 2.9%. cTBFTBCB exhibits strong absorption from 400 - 500 nm, as well as at 550 nm. This material has the narrowest optical band gap of any contorted PAH reported thus far and shows promise for applications in OPVs.