Solid-state dye sensitized solar cells with conducting polymers as hole transporting medium

International Conference on Hybrid and Organic Photovoltaics
Proceedings of International Conference on Hybrid and Organic Photovoltaics 2015 (HOPV15)

Poster, Jinbao Zhang, 290
Publication date: 5th February 2015

Conducting polymers directly deposited into the porous structure of dye-coated TiO₂ electrodes by in-situ photoelectrochemical polymerization (PEP) have the advantage of easy penetration and complete pore infiltration over other small molecular hole conductors used in solid-state dye-sensitized solar cells (SDSCs). Besides, the remarkably high hole conductivity and stability make it a competitor to the usual alternatives, redox mediator-containing  liquid electrolytes  or small-molecule hole conductors, as DSSC charge-transport media. The focus has been directed in four particular aspects. At first, an aqueous micellar electrolyte, instead of the usual organic solution, was demonstrated to be possible to use in PEP to generate PEDOT from bisEDOT precursor [1]. The advantage of aqueous PEP over organic PEP is not only the relatively inexpensive and environment-friendly character of the process, but also the less-positive oxidation potentials of precursor in aqueous solution, thereby increasing the driving force for the PEP. The SDSCs  based on PEDOT generated from aqueous PEP shows a power conversion efficiency (PCE) of 5.2% with an organic sensitizer, as compared to 5.6% for the device based on organic PEP [2]. By comparison of the PEDOT properties for layers generated from the two approaches, PEDOT with shorter polymer chains in aqueous PEP led to better dye regeneration but faster charge recombination in the devices. A second direction of work is to use the less expensive monomer EDOT as precursor to replace bisEDOT. The PEP of EDOT was first time achieved in aqueous electrolyte due to the much lower oxidation potential than that in organic solution, where PEP is difficult; the corresponding SDSCs exhibit 3% 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 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 side, the dyes’ blocking effect variations, due to  different chemical structure, play a significant role on the interfacial charge recombination; on the other hand, the redox potentials of the dyes could affect the rate of PEP and the final polymer properties. By effectively combination of organic dye LEG4 and PEDOT hole conductor, a PCE of 7.1% has been recently obtained.

[1]Yang, L., Zhang, J., Shen, Y., Park, B., J. Phys. Chem. Lett., 2013, 4 (23), pp 4026–4031 [2]Zhang, J., Yang, L., Shen, Y., Park, B., Hao, Y. et al. Poly(3,4-ethylenedioxythiophene) Hole-Transporting Material Generated by Photoelectrochemical Polymerization in Aqueous and Organic Medium for All-Solid-State Dye-Sensitized Solar Cells. The Journal of Physical Chemistry C, 118(30): 16591-16601 [3] Zhang, J., Häggman, L., Jouini, M., Jarboui, A., Boschloo, G. et al. Solid-State Dye-Sensitized Solar Cells Based on Poly(3,4ethylenedioxypyrrole) and Metal-Free Organic Dyes. ChemPhysChem, 15(6): 1043-1047 [4] Zhang, J., Jarboui, A., Vlachopoulos, N., Jouini, M., Boschloo, G., Hagfeldt, A., Photoelectrochemical Polymerization of EDOT for Solid State Dye Sensitized Solar Cells: Role of Dye and Solvent, Electrochimica Acta. doi:10.1016/j.electacta.2015.01.077

© FUNDACIO DE LA COMUNITAT VALENCIANA SCITO