Conductivity Enhancement of PEDOT:PSS via Addition of Chloroplatinic Acid and Its Mechanism

Readily obtained highly conductive, transparent, and flexible poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) films is urgently needed in printing of flexible transparent electrodes. A simple and facile method to enhance the electrical conductivity of PEDOT:PSS films is reported. The conductivity is increased by four orders of magnitude after adding solid chloroplatinic acid (H2PtCl6) into the pristine PEDOT:PSS solution. The H2PtCl6-doped PEDOT:PSS film exhibits a sheet resistance of 44 +/- 5 Omega square(-1) and a transmittance of 84 +/- 1% at 550 nm, corresponding to a figure of merit of 47 +/- 4. Comparative study shows addition of solid acid like H2PtCl6 is more effective in conductivity enhancement than addition of polar organic solvents, such as dimethyl sulfoxide or ethylene glycol. The mechanism for the conductivity enhancement is attributed to both in situ doping and phase separation of PEDOT:PSS. PEDOT is oxidized and doped by Pt4+ of H2PtCl6, which is reduced simultaneously to Pt2+. Proton transfer from H2PtCl6 to PSS- of PEDOT:PSS causes formation of neutral PSSH, leading to phase separation between insulating PSS and conducting PEDOT. Such a phase separation results in conformational changes of PEDOT chains and reduction in energy barrier for charge hopping.