Conducting polymer- based hole conductors (HCs), directly deposited into the mesoporous structure of dye-coated TiO2 electrodes by the in-situ photoelectrochemical polymerization (PEP) method, have the advantage of easy penetration and uniform pore infiltration compared to small molecular HCs used in solid-state dye-sensitized solar cells (sDSCs). These advantages of conducting polymer-based HCs from PEP would lead to an efficient charge separation at the interfaces between TiO2/dye/HCs. The present work has been directed toward the study of the influence of the  PEP parameters on the solar cell properties. At first, the use of an aqueous micellar electrolyte, instead of the usual organic solution, was demonstrated to generate PEDOT HC from a bisEDOT precursor. Aqueous PEP (A-PEP)  is not only environment-friendly but also has the advantage of a   less-positive oxidation potential compared to organic PEP (O-PEP), so that PEP is facilitated. An A-PEP-based  SDSC shows a power conversion efficiency (PCE) of 5.2% with an organic sensitizer, as compared to 5.6% for the O-PEP-based S-DSC. A second direction of work is the replacement of bis-EDOT with monomer EDOT, the A-PEP of which  was achieved for the first time, taking advantage of the much lower oxidation potential in aqueous than in organic solution, with a  3.0% efficiency. Thirdly, an alternative monomer, EDOP, was efficiently used in PEP by combining with organic dyes. The devices based on the PEDOP hole conductor have a PCE of 4.5%; this level of performance, achieved for the first time for PEDOP-based sDSCs, is attributed to the high hole conductivity of PEDOP and the good blocking effect from organic dyes. At last, the importance of the dyes’ chemical structure and energy levels on the PEP has been systematically investigated. It is shown that, on one hand, the dyes’ blocking effect variations, due to the different chemical structure, play a significant role on the interfacial charge recombination; on the other hand, the dye redox potential could affect the kinetics of the PEP process and the final polymer properties. By effectively combination of an organic dye LEG4 and the formed PEDOT HC, a PCE of 7.1% with a record current (13.4 mAcm-2) has been recently obtained for sDSCs. The impressive photovoltaic performance was attributed to the high hole conductivity of PEDOT (2.0 Scm-1) obtained from PEP, as well as the effective dye blocking effect, leading to a high yield of charge collection.

References

[1] Vlachopoulos, N., Zhang, J., Hagfeldt, A., Chimia, 2015, 69, 41-51

[2] Zhang, J., Yang, L., Shen, Y., et al.,   J. Phys.Chem.C 2014, 118, 16591-16601