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

F. Hinkel, Y.M. Kim, Y. Zagraniarsky, F. Schlütter, D. Andrienko, K. Müllen, F. Laquai
The Journal of Chemical Physics, 148 (4), 044703, (2018)

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

Keywords

Charge generation, Efficient electron injection, Electron-hole recombination, Photoinduced absorption, Quasi-steady state, Recombination process, Solid-state dye-sensitized solar cells, Transient absorption

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.

Code

DOI: 10.1063/1.4999136

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