Metal-free branched alkyl tetrathienoacene (TTAR)-based sensitizers for high-performance dye-sensitized solar cells

Yamuna Ezhumalai; Byunghong Lee; Miao-Syuan Fan; Boris Harutyunyan; Kumaresan Prabakaran; Chuan-Pei Lee; Sheng Hsiung Chang; Jen-Shyang Ni; Sureshraju Vegiraju; Pragya Priyanka; Ya-Wen Wu; Chia-Wei Liu; Shuehlin Yau; Jiann T. Lin; Chun-Guey Wu; Michael J. Bedzyk; Robert P. H. Chang; Ming-Chou Chen; Kuo-Chuan Ho; Tobin J. Marks

doi:10.1039/C7TA01825H

Metal-free branched alkyl tetrathienoacene (TTAR)-based sensitizers for high-performance dye-sensitized solar cells†

Yamuna Ezhumalai,‡^a Byunghong Lee,

‡^b Miao-Syuan Fan,‡^c Boris Harutyunyan,‡^d Kumaresan Prabakaran,‡^ae Chuan-Pei Lee,^c Sheng Hsiung Chang,^f Jen-Shyang Ni,^g Sureshraju Vegiraju,^a Pragya Priyanka,^a Ya-Wen Wu,^a Chia-Wei Liu,^a Shuehlin Yau,^a Jiann T. Lin,

^g Chun-Guey Wu,

^af Michael J. Bedzyk,*^dh Robert P. H. Chang,*^b Ming-Chou Chen,

*^a Kuo-Chuan Ho*^c and Tobin J. Marks

*ⁱ

Author affiliations

* Corresponding authors

^a Department of Chemistry, National Central University, Chung-Li-32054, Taiwan
E-mail: mcchen@ncu.edu.tw

^b Materials Research Institute, Northwestern University, Evanston, IL 60208, USA

^c Department of Chemical Engineering, National Taiwan University, Taipei 10617, Taiwan
E-mail: kcho@ntu.edu.tw

^d Department of Physics, Astronomy and the Argonne-Northwestern Solar Energy Research Center, Northwestern University, Evanston, Illinois 60208, USA

^e Department of Chemistry, PSG College of Arts and Science, Coimbatore-641014, India

^f Research Center for New Generation Photovoltaics, National Central University, Chung-Li 32054, Taiwan

^g Institute of Chemistry, Academia Sinica, Nankang, Taipei 11529, Taiwan

^h Department of Materials Science and Engineering, The Argonne-Northwestern Solar Energy Research Center, Northwestern University, Evanston, Illinois 60208, USA

ⁱ Department of Chemistry, The Materials Research Center, The Argonne-Northwestern Solar Energy Research Center, Northwestern University, Evanston, Illinois 60208, USA
E-mail: t-marks@northwestern.edu

Abstract

A new series of metal-free alkylated tetrathienoacene (TTAR)-based organic chromophores, TPA–TTAR–TA (R = branched-C₈H₁₇, 1, TTAR-b8; R = C₁₅H₃₁, 2, TTAR-15; R = C₉H₁₉, 3, TTAR-9), are synthesized for application in dye-sensitized solar cells (DSSCs). Due to the extensively conjugated TTAR π-bridge, all three dyes exhibit high extinction coefficients (1 × 10⁵ M⁻¹ cm⁻¹). By systematically exploring the effects of the TTAR alkyl chain substituents, a significant influence of the dye coverage (orientation) on the TiO₂ surfaces is observed. The branched-alkyl TTAR-b8 (1) promotes significant tilting and packing distortion on TiO₂ in comparison to more ordered monolayers of linear long alkyls TTAR-15 (2) and TTAR-9 (3). Photophysical measurements on the dye-grafted TiO₂ films reveal that the branched-alkylated TTA unit in 1 enhances the electron injection efficiency, in agreement with the high quantum efficiency. Notably, by utilizing a three-dimensional (3D) photonic crystal (PhC) layer to enhance the coherent scattering an increase the light absorption, TTAR-b8 exhibits higher short-circuit current densities and achieved a high PCE of 11.18%. TTAR-b8 is thus the best performing fused-thiophene-based organic DSSC dye reported to date.

Journal of Materials Chemistry A

Metal-free branched alkyl tetrathienoacene (TTAR)-based sensitizers for high-performance dye-sensitized solar cells†

Abstract

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