Molecular engineering of simple phenothiazine-based dyes to modulate dye aggregation, charge recombination, and dye regeneration in highly efficient dye-sensitized solar cells

Yong Hua; Shuai Chang; Jian He; Caishun Zhang; Jianzhang Zhao; Tao Chen; Wai-Yeung Wong; Wai-Kwok Wong; Xunjin Zhu

doi:10.1002/chem.201304897

Molecular engineering of simple phenothiazine-based dyes to modulate dye aggregation, charge recombination, and dye regeneration in highly efficient dye-sensitized solar cells

Chemistry. 2014 May 19;20(21):6300-8. doi: 10.1002/chem.201304897. Epub 2014 Apr 8.

Authors

Yong Hua¹, Shuai Chang, Jian He, Caishun Zhang, Jianzhang Zhao, Tao Chen, Wai-Yeung Wong, Wai-Kwok Wong, Xunjin Zhu

Affiliation

¹ Department of Chemistry and Institute of Advanced Materials, Institute of Molecular Functional Materials and HKBU, Institute of Research and Continuing Education (Shenzhen), Hong Kong Baptist University, Waterloo Road, Kowloon Tong, Hong Kong (S.A.R. China), Fax: (+86) 852-3411-7348.

PMID: 24715494
DOI: 10.1002/chem.201304897

Abstract

A series of simple phenothiazine-based dyes, namely, TP, EP, TTP, ETP, and EEP have been developed, in which the thiophene (T), ethylenedioxythiophene (E), their dimers, and mixtures are present to modulate dye aggregation, charge recombination, and dye regeneration for highly efficient dye-sensitized solar cell (DSSC) applications. Devices sensitized by the dyes TP and TTP display high power conversion efficiencies (PCEs) of 8.07 (Jsc = 15.2 mA cm(-2), Voc =0.783 V, fill factor (FF) = 0.679) and 7.87 % (Jsc = 16.1 mA cm(-2), Voc = 0.717 V, FF = 0.681), respectively; these were measured under simulated AM 1.5 sunlight in conjunction with the I(-)/I3(-) redox couple. By replacing the T group with the E unit, EP-based DSSCs had a slightly lower PCE of 7.98 % with a higher short-circuit photocurrent (Jsc) of 16.7 mA cm(-2). The dye ETP, with a mixture of E and T, had an even lower PCE of 5.62 %. Specifically, the cell based on the dye EEP, with a dimer of E, had inferior Jsc and Voc values and corresponded to the lowest PCE of 2.24 %. The results indicate that the photovoltaic performance can be finely modulated through structural engineering of the dyes. The selection of T analogues as donors can not only modulate light absorption and energy levels, but also have an impact on dye aggregation and interfacial charge recombination of electrons at the interface of titania, electrolytes, and/or oxidized dye molecules; this was demonstrated through DFT calculations, electrochemical impedance analysis, and transient photovoltage studies.

Keywords: aggregation; charge recombination; dyes/pigments; phenothiazine; solar cells.