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A Comparative Study of the Influence of N,N'-dialkyl vs N,N'-diaryl based Electron Donors Ancillary Ligands on the Photocurrent and Photovoltage in Dye-Sensitized Solar Cells (DSSCs)

Abstract

In this work, we report the synthesis of a novel heteroleptic Ru(II)-sensitizer namely Ru(2,2'-bipyridine-4,4'-dicarboxylic acid)-4,4'-bis(4-piperidin-1-yl)phenyl ethenyl)-2,2'-bipyridine) (NCS)2 denoted as SD-1 and its photophysical, electrochemical and photovoltaic performance were compared to N719 and K77-7 (N,N'-diaryl Ru-sensitizer namely Ru(2,2'-bipyridine-4,4'- dicarboxylic-acid)-4,4'-bis(2-(4-N,N'-diphenylaminophenyl)ethenyl)-2,2'-bipyridine) (NCS)2). The photovoltaics performance of SD-1 outperformed that of N-719 and K77-7, particularly in the red region, with overall efficiency of 8.5% compared to 8.0% of K77-7 and 7.7% of N719 under the same experimental device conditions. The superior light harvesting efficiency of SD-1 can be attributed to the stronger electron donor of sp3-nitrogen, which is attached to two sp3-carbons (dialkyl), where in the case of K77-7 all carbons attached to the sp3-nitrogen are sp2, which decreases the electron density on the latter and minimize electron donatin power of the ancillary ligand in K77-7. To gain quantitative understanding of the electron density on the nitrogen in SD-1 and K77-7, first principle calculations using molecular and thermodynamic descriptors such as frontier molecular orbitals, ground state oxidation potential (GSOP), excited state oxidation potential (ESOP), optical gap (E0-0), and charge distributions were calculated in solution as well as for the anchored structures of dyes onto Ti24O48 utilizing density functional theory (DFT) and time-dependent density functional theory (TD-DFT). Results of computational studies were in excellent agreement with experimental results, which can be used as a screening tool for the design of more efficient molecular motifs for DSSCs.

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Publication details

The article was received on 18 Apr 2017, accepted on 06 Jul 2017 and first published on 06 Jul 2017


Article type: Paper
DOI: 10.1039/C7CP02530K
Citation: Phys. Chem. Chem. Phys., 2017, Accepted Manuscript
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    A Comparative Study of the Influence of N,N'-dialkyl vs N,N'-diaryl based Electron Donors Ancillary Ligands on the Photocurrent and Photovoltage in Dye-Sensitized Solar Cells (DSSCs)

    S. Ashraf, E. Yildirim, J. Akhtar, H. M. Siddiqi and A. M. El-Shafei, Phys. Chem. Chem. Phys., 2017, Accepted Manuscript , DOI: 10.1039/C7CP02530K

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