LAUSR

Abstract Highly regioregular poly(3-hexylthiophene) derivatives with varying degrees of fluorine substitution on the thiophene moieties have been demonstrated in photovoltaic devices and characterized using ultraviolet and inverse photoelectron spectroscopy. As fluorine content is increased, an increase in ionization energy of 0.3 eV is observed for 50% fluorination compared to non-fluorinated poly(3-hexylthiophene). The electron affinity is observed to increase to a lesser extent with increased fluorination, consistent with a systematic increase in the optical bandgaps of up to 0.12 eV. Bulk heterojunction photovoltaic devices made from polymer:PC 61 BM blends achieve power conversion efficiencies of 3%, however film morphologies measured using atomic force microscopy indicate that strong phase separation with increasing fluorination limits device performance. UV–vis spectra of thin films of the fluorinated materials exhibit a long tail in the red, extending to longer wavelengths than non-fluorinated poly(3-hexylthiophene). Photovoltaic devices similarly exhibit non-zero quantum efficiency in this region. This behavior has been attributed to a low energy, interchain charge transfer state.