Influence of Doped Anions on Poly(3,4-ethylenedioxythiophene) as Hole Conductors for Iodine-Free Solid-State Dye-Sensitized Solar Cells

Abstract

Poly(3,4-ethylenedioxythiophene) (PEDOT) is an excellent hole-conducting polymer able to replace the liquid I^-/I₃^- redox electrolyte in dye-sensitized solar cells (DSCs). In this work we applied the in situ photoelectropolymerization technique to synthesize PEDOT and carried out a careful analysis of the effect of different doping anions on overall solar cell performance. The anions analyzed in this work are ClO₄^-, CF₃SO₃^-, BF₄^-, and TFSI⁻. The best solar cell performance was observed when the TFSI^- anion was used. Photoelectrochemical and impedance studies reveal that the doped anions in the PEDOT hole conductor system have great influences on I−V curves, conductivity, and impedance. The optimization of these parameters allowed us to obtain an iodine-free solid-state DSC with a maximum J_sc of 5.3 mA/cm², V_oc of 750 mV, and a conversion efficiency of 2.85% which is the highest efficiency obtained so far for an iodine-free solid-state DSC using PEDOT as hole-transport material.