Poly(3,4-ethylenedioxythiophene) Hole-Transporting Material Generated by Photoelectrochemical Polymerization in Aqueous and Organic Medium for All-Solid-State Dye-Sensitized Solar Cells

We applied organic donor-pi-acceptor (D-pi-A) sensitizers for photoelectrochemical polymerization (PEP) because of their appropriate energy levels and high light absorption. The polymerized conducting polymer PEDOT was used as hole conductor in all-solid-state dye-sensitized solar cells (ssDSCs). By combination of the D-pi-A sensitizers and the generated PEDOT from PEP of bis-EDOT in acetonitrile, the resulting device showed an average power conversion efficiency of 5.6%. Furthermore, the PEP in aqueous micellar electrolytic medium was also employed because of the ability to decrease oxidation potential of the precursor, thereby making the polymerization process easier. The latter method is a cost-effective and environmentally friendly approach. Using as hole conductor the so-obtained PEDOT from PEP of bis-EDOT in aqueous electrolyte, the devices exhibited impressive power conversion efficiency of 5.2%. To compare the properties of the generated polymer from bis-EDOT in these two PEP methods, electron lifetime, photoinduced absorption (PIA) spectra, and UV-vis-NIR spectra were measured. The results showed that PEDOT from organic PEP exhibits a delocalized conformation with high conductivity and a smooth and compact morphology; a rough morphology with high porosity and polymer structure of relatively shorter chains was assumed to be obtained from aqueous PEP. Therefore, better dye regeneration but faster charge recombination was observed in the device based on PEDOT from aqueous PEP of bis-EDOT. Subsequently, to extend the aqueous PEP approach in consideration of the ability to decrease the oxidation potential of the precursor, the easily available precursor EDOT was for the first time used for PEP in aqueous medium in a variant of the aforementioned procedure, and the device based on the so-obtained PEDOT shows a more than 70-fold increase in efficiency, 3.0%, over that based on the polymer generated from EDOT by PEP in organic media. It was demonstrated that aqueou