Efficiency-limiting processes in cyclopentadithiophene-bridged donor-acceptor-type dyes for solid-state dye-sensitized solar cells

Abstract
The charge generation and recombination processes in three novel push-pull photosensitizers for dye-sensitized solar cells (DSSCs) are studied by ps–μs transient absorption (TA) and quasi-steady-state photoinduced absorption (PIA) spectroscopy. The three cyclopentadithiophene-based photosensitizer dye molecules exhibit comparably low power conversion efficiencies ranging from 0.8% to 1.7% in solid-state DSSCs. We find that the photocurrents increase in the presence of Li-salt additives. Both TA and PIA measurements observe long-lived dye cations created by electron injection from the dyes’ excited state for two dyes from the series. However, the third dye shows significantly lower performance as a consequence of the less efficient electron injection even after the addition of Li-salts and faster electron-hole recombination on the ns-μs time scale. In essence, the prerequisites for this class of donor-π bridge-acceptor photosensitizers to reach higher charge generation efficiencies are a combination of strong dipole moments and fine tuning of the electronic landscape at the titania-dye interface by Li-salt addition.

Citation
Hinkel F, Kim YM, Zagraniarsky Y, Schlütter F, Andrienko D, et al. (2018) Efficiency-limiting processes in cyclopentadithiophene-bridged donor-acceptor-type dyes for solid-state dye-sensitized solar cells. The Journal of Chemical Physics 148: 044703. Available: http://dx.doi.org/10.1063/1.4999136.

Acknowledgements
F. Laquai thanks the Max Planck Society for funding the Max Planck Research Group.

Publisher
AIP Publishing

Journal
The Journal of Chemical Physics

DOI
10.1063/1.4999136

Additional Links
http://aip.scitation.org/doi/10.1063/1.4999136

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