Fluorination of polythiophene derivatives for high performance organic photovoltaics

For the purpose of examining the tuning of photophysical property by fluorine atom substitution, fluorinated and nonfluorinated poly(3,4- dialkylterthiophenes) (PDATs) were synthesized, and their photovoltaic properties were compared. Fluorinated PDATs exhibit a deeper highest occupied molecular orbital energy level than nonfluorinated ones, leading to higher open-circuit voltage in organic solar cells and also enhanced molecular ordering as evidenced by a vibronic shoulder in UV-vis spectra, π-π scattering in GIWAXS, and a well-developed fibril structure in TEM, which contributes to efficient charge transport. As a result, the fluorine substitution increases the power conversion efficiency by 20% to 250% as compared with nonfluorinated PDATs.