An Integrated Experimental/Theoretical Study of Structurally Related Poly-Thiophenes Used in Photovoltaic Systems

In this work, a series of eight thiophene-based polymers (exploited as “donors” in bulk
heterojunction photovoltaics cells), whose structures were designed to be suitably tuned with the
electronic characteristics of the [6,6]-Phenyl C61 butyric acid methyl ester (PCBM), is considered,.
The electronic properties of the mono-, di-, trimeric oligomers are reckoned (at the Hartree-Fock
and DFT level of the theory) and compared to experimental spectroscopic and electrochemical
results. Indeed, electrochemical and spectroscopic results show a systematic difference whose
physical nature is assessed and related to the exciton (electron-hole) binding energy (Je,h). The
critical comparison of the experimental and theoretical band gaps, i.e., the HOMO-LUMO energy
difference, suggests that electrochemical and DFT values are the most suited to being used in the
design of a polythiophene-based p-n junction for photovoltaics.