Acta Phys. -Chim. Sin. ›› 2016, Vol. 32 ›› Issue (1): 329-336.doi: 10.3866/PKU.WHXB201511031

• ARTICLE • Previous Articles     Next Articles

Ultrafast Spectroscopic Studies of Excited State Relaxation and Electron Injection in Organic Dye-Sensitized Solar Cells

Lin YANG1,2,Yang LI1,2,Shu CHEN1,2,Jing ZHANG1,Min ZHANG1,*(),Peng WANG1   

  1. 1 State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, P.R.China
    2 University of Chinese Academy of Sciences, Beijing 100049, P.R.China
  • Received:2015-10-02 Published:2016-01-13
  • Contact: Min ZHANG E-mail:min.zhang@ciac.ac.cn
  • Supported by:
    the National Natural Science Foundation of China(51473158, 91233206, 51125015)

Abstract:

Unlocking the dynamics of the evolution of the excited state at the complicated titania/dye/ electrolyte interface in organic dye-sensitized solar cells is crucial to provide a basis for the rational design of low-energy-gap organic photosensitizers.By constructing two organic donor-acceptor dyes composed of benzothiadiazole-benzoic acid (BTBA) and pyridothiadiazole-benzoic acid (PTBA) as electron acceptors, we have identified the images of multiple-step relaxations of the excited state and multiple-state electron injections at the titania/dye/electrolyte interface using ultrafast transient absorption spectroscopic measurements in conjunction with theoretical simulations.Density functional theory and time-dependent density functional theory calculations indicate that there should be torsion-induced excited state relaxations from an optically generated"hot"excited state to the equilibrium excited state characteristic of a more planar conjugated backbone and a quinonoid structure for dye molecules on the titania surface, suggesting the probable presence of multiple-state electron injections at the titania/dye/electrolyte interface.In virtue of a target analysis of femtosecond transient absorption spectra, we have found that the dye with PTBA features a much lower overall electron injection yield with respect to the dye with BTBA owing to the sluggish electron injection and short lifetime of the excited state, accounting for a lower maximum of external quantum efficiencies of the device made from the dye with PTBA as an acceptor.

Key words: Solar cell, Organic dye, Interface, Excited state, Charge transfer

MSC2000: 

  • O644