Acta Phys. -Chim. Sin. ›› 2012, Vol. 28 ›› Issue (01): 78-84.doi: 10.3866/PKU.WHXB20122878


Comparison of D-SS and D-ST Dyes as Photo Sensitizers in Dye-Sensitized Solar Cells

ZHAN Wei-Shen, PAN Shi, WANG Qiao, LI Hong, ZHANG Yi   

  1. Institute of Near-Field Optics and Nanotechnology, School of Physics and Optoelectronic Technology, Dalian University of Technology, Dalian 116024, Liaoning Province, P. R. China
  • Received:2011-06-10 Revised:2011-11-07 Published:2011-12-29
  • Contact: PAN Shi

Abstract: The molecular structures, UV-Vis absorption spectra, and energy level structures of the dyes D-SS and D-ST were simulated using density functional theory, time-dependent density functional theory (TDDFT), and natural bond orbital analysis, which provided the physical mechanisms of dye-sensitized solar cells (DSSCs) containing D-ST and D-SS. The UV-Vis absorption spectrum of D-SS showed a significant red shift compared with that of D-ST and the molar absorption coefficient of D-SS was higher than that of D-ST. D-SS molecules should have a higher solar radiation photon-harvesting ability than D-ST molecules, but the energy level of the highest occupied molecular orbital (HOMO) of D-SS was higher than the redox energy level of the electrolyte (I-/I3-). As a result, an optically excited D-SS molecule cannot be successfully recovered by accepting an electron from the electrolyte after being oxidized by injecting an electron towards the TiO2 electrode. This limits the photon harvesting ability of D-SS molecules, and thereby significantly decreases the photovoltaic properties and energy conversion efficiency of DSSCs containing D-SS. This allows the photovoltaic properties of DSSCs containing D-SS to be understood, especially why its photovoltaic energy conversion efficiency is lower than that of DSSCs containing D-ST. The position of the HOMO energy level of dye-sensitized molecules is very important for the operation of DSSCs, and that of the organic sensitizer molecules used in DSSCs must be lower than the redox energy level of the electrolyte.

Key words: Density functional theory, Time-dependent density functional theory, Dye-sensitized solar cells, Molecular simulation, Electronic structure, Absorption spectrum, Energy level


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