Effect of Wetting Surfactants on the Work Function of PEDOT:PSS for Organic Solar Cells

Solution-processable poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a widely used hole transporting layer (HTL) in organic solar cells (OSCs). However, it is a challenge to adopt it as the HTL on hydrophobic active layers to fabricate inverted OSCs. Surfactants are generally added to improve the wettability of aqueous PEDOT:PSS. In this work, we report that surfactants could induce a change in the work function (WF) of PEDOT:PSS and significantly influence the device performance. Fluorine-containing surfactants could deliver higher device performance than fluorine-free surfactants because the fluorine-free surfactants decrease the WF of PEDOT:PSS, which results in poor electrical contact between the WF of PEDOT:PSS and the highest occupied molecular orbital (HOMO) level of the polymer donor of the active layer. With the fluorine-containing surfactants, we deposited aqueous PEDOT:PSS on the hydrophobic active layer with good film quality and high WF and further fabricated inverted OSCs with comparable performance to the reference device with evaporated MoO3 ( )as the HTL.