The Role of Mineral Acid Doping of PEDOT:PSS and Its Application in Organic Photovoltaics

Poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) is one of the most successful conducting polymers in terms of commercialization. A method to readily obtain highly conductive and transparent PEDOT:PSS films is urgently needed. A simple method is introduced to enhance the conductivity of such films dramatically. By adding a series of mineral acids into the PEDOT:PSS aqueous solution directly, the conductivity is enhanced by 3-4 orders of magnitude. Mechanistic study reveals that the conductivity enhancement is dependent on boiling point, pK(a) value, softness parameter, and oxidability of the dopant acid. Specifically, acids with high boiling point, low pK(a), and low softness parameter are able to induce phase separation between PEDOT and PSS, leading to secondary doping. If the dopant acid exhibits strong oxidability, the conductivity can also be enhanced via primary doping. H2SO4-doped PEDOT:PSS films exhibit the highest conductivity of 2244 S cm(-1). These films are employed as the transparent electrodes of poly(3-hexylthiophene-2,5-diyl) (P3HT)-based organic photovoltaic cells, and the power conversation efficiency reaches 3.13%. These results suggest direct acid doping of PEDOT:PSS solution is a facile approach to obtain highly flexible transparent electrodes.