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ACS Appl Mater Interfaces. 2017 Oct 11;9(40):34812-34820. doi: 10.1021/acsami.7b08098. Epub 2017 Oct 2.

Molecular Engineering for Enhanced Charge Transfer in Thin-Film Photoanode.

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Department of Chemistry, Ulsan National Institute of Science and Technology , Ulsan, 689-798, Republic of Korea.
School of Energy and Chemical Engineering, Ulsan National Institute of Science and Technology , Ulsan, 689-798, Republic of Korea.


We developed three types of dithieno[3,2-b;2',3'-d]thiophene (DTT)-based organic sensitizers for high-performance thin photoactive TiO2 films and investigated the simple but powerful molecular engineering of different types of bonding between the triarylamine electron donor and the conjugated DTT π-bridge by the introduction of single, double, and triple bonds. As a result, with only 1.3 μm transparent and 2.5-μm TiO2 scattering layers, the triple-bond sensitizer (T-DAHTDTT) shows the highest power conversion efficiency (η = 8.4%; VOC = 0.73 V, JSC = 15.4 mA·cm-2, and FF = 0.75) in an iodine electrolyte system under one solar illumination (AM 1.5, 1000 W·m-2), followed by the single-bond sensitizer (S-DAHTDTT) (η = 7.6%) and the double-bond sensitizer (D-DAHTDTT) (η = 6.4%). We suggest that the superior performance of T-DAHTDTT comes from enhanced intramolecular charge transfer (ICT) induced by the triple bond. Consequently, T-DAHTDTT exhibits the most active photoelectron injection and charge transport on a TiO2 film during operation, which leads to the highest photocurrent density among the systems studied. We analyzed these correlations mainly in terms of charge injection efficiency, level of photocharge storage, and charge-transport kinetics. This study suggests that the molecular engineering of a triple bond between the electron donor and the π-bridge of a sensitizer increases the performance of dye-sensitized solar cell (DSC) with a thin photoactive film by enhancing not only JSC through improved ICT but also VOC through the evenly distributed sensitizer surface coverage.


bonding effect; charge injection; intramolecular charge transfer; molecular engineering; self-aggregation


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