Influence of electrolyte cations on electron transport and electron transfer in dye-sensitized solar cells

The influence of different electrolyte cations ((Li+, Na+, Mg2+, tetrabutyl ammonium (TBA+)) on the TiO2 conduction band energy (Ec) the effective electron lifetime (τn), and the effective electron diffusion coefficient (Dn) in dye-sensitized solar cells (DSCs) was studied quantitatively. The separation between Ec and the redox Fermi level, EF,redox, was found to decrease as the charge/radius ratio of the cations increased. Ec in the Mg2+ electrolyte was found to be 170 meV lower than that in the Na+ electrolyte and 400 meV lower than that in the TBA+ electrolyte. Comparison of Dn and τn in the different electrolytes was carried out by using the trapped electron concentration as a measure of the energy difference between Ec and the quasi-Fermi level, nEF, under different illumination levels. Plots of Dn as a function of the trapped electron density, nt, were found to be relatively insensitive to the electrolyte cation, indicating that the density and energetic distribution of electron traps in TiO2 are similar in all of the electrolytes studied. By contrast, plots of τn versus nt for the different cations showed that the rate of electron back reaction is more than an order of magnitude faster in the TBA+ electrolyte compared with the Na+ and Li+ electrolytes. The electron diffusion lengths in the different electrolytes followed the sequence of Na+ > Li+ > Mg2+ > TBA+. The trends observed in the AM 1.5 current–voltage characteristics of the DSCs are rationalized on the basis of the conduction band shifts and changes in electron lifetime.

[1]  David Emin,et al.  High mobility n‐type charge carriers in large single crystals of anatase (TiO2) , 1994 .

[2]  Donald Fitzmaurice,et al.  ELECTRON ACCUMULATION IN NANOSTRUCTURED TIO2 (ANATASE) ELECTRODES , 1999 .

[3]  Min Zhang,et al.  Influences of cation charge density on the photovoltaic performance of dye-sensitized solar cells: lithium, sodium, potassium, and dimethylimidazolium. , 2011, Physical chemistry chemical physics : PCCP.

[4]  Xudong Yang,et al.  Effects of 4-tert-butylpyridine on the quasi-Fermi levels of TiO2 films in the presence of different cations in dye-sensitized solar cells. , 2011, Physical chemistry chemical physics : PCCP.

[5]  J. Bell,et al.  Kinetics of electron recombination of dye-sensitized solar cells based on TiO2 nanorod arrays sensitized with different dyes. , 2011, Physical chemistry chemical physics : PCCP.

[6]  M. Grätzel,et al.  A low-cost, high-efficiency solar cell based on dye-sensitized colloidal TiO2 films , 1991, Nature.

[7]  Laurence M. Peter,et al.  A Reappraisal of the Electron Diffusion Length in Solid-State Dye-Sensitized Solar Cells , 2007 .

[8]  C. Olson.  Influence of cation on charge recombination in dye-sensitized TiO2 electrodes. , 2006, The journal of physical chemistry. B.

[9]  Eric A. Schiff,et al.  Ambipolar Diffusion of Photocarriers in Electrolyte-Filled, Nanoporous TiO2† , 2000 .

[10]  S. Pelet,et al.  Cooperative Effect of Adsorbed Cations and Iodide on the Interception of Back Electron Transfer in the Dye Sensitization of Nanocrystalline TiO2 , 2000 .

[11]  Alison B. Walker,et al.  Dye-sensitized solar cells based on oriented TiO2 nanotube arrays: transport, trapping, and transfer of electrons. , 2008, Journal of the American Chemical Society.

[12]  Takayuki Kitamura,et al.  Role of electrolytes on charge recombination in dye-sensitized TiO(2) solar cell (1): the case of solar cells using the I(-)/I(3)(-) redox couple. , 2005, The journal of physical chemistry. B.

[13]  Anders Hagfeldt,et al.  Activation energy of electron transport in dye-sensitized TiO2 solar cells. , 2005, The journal of physical chemistry. B.

[14]  David F. Watson,et al.  Cation effects in nanocrystalline solar cells , 2004 .

[15]  Adrian C. Fisher,et al.  Intensity Dependence of the Back Reaction and Transport of Electrons in Dye-Sensitized Nanocrystalline TiO2 Solar Cells , 2000 .

[16]  John M. Bell,et al.  Effect of Inorganic Iodides on Performance of Dye-Sensitized Solar Cells , 2007 .

[17]  Laurence M. Peter,et al.  How Efficient Is Electron Collection in Dye-Sensitized Solar Cells? Comparison of Different Dynamic Methods for the Determination of the Electron Diffusion Length , 2009 .

[18]  Y. Wada,et al.  Investigation of cation-induced degradation of dye-sensitized solar cells for a new strategy to long-term stability. , 2005, Langmuir : the ACS journal of surfaces and colloids.

[19]  Donald Fitzmaurice,et al.  Spectroscopic determination of flatband potentials for polycrystalline titania electrodes in nonaqueous solvents , 1993 .

[20]  Laurence M. Peter,et al.  Characterization and Modeling of Dye-Sensitized Solar Cells , 2007, ECS Transactions.

[21]  J. Durrant,et al.  Parameters influencing the efficiency of electron injection in dye-sensitized solar cells. , 2009, Journal of the American Chemical Society.

[22]  Anders Hagfeldt,et al.  The influence of cations on charge accumulation in dye-sensitized solar cells , 2007 .

[23]  L. Peter,et al.  Frequency-Resolved Optical Detection of Photoinjected Electrons in Dye-Sensitized Nanocrystalline Photovoltaic Cells , 1999 .

[24]  Juan Bisquert,et al.  Interpretation of the Time Constants Measured by Kinetic Techniques in Nanostructured Semiconductor Electrodes and Dye-Sensitized Solar Cells , 2004 .

[25]  L. Peter,et al.  Direct measurement of the temperature coefficient of the electron quasi-fermi level in dye-sensitized nanocrystalline solar cells using a titanium sensor electrode. , 2006, The journal of physical chemistry. B.

[26]  C. Kelly,et al.  Cation-Controlled Interfacial Charge Injection in Sensitized Nanocrystalline TiO2 , 1999 .

[27]  K. Tada,et al.  Preparation of Large-Size Anisotropic Polypyrrole Film and Its Actuation Property , 2003 .

[28]  Jingyuan Liu,et al.  Synchronously reduced surface states, charge recombination, and light absorption length for high-performance organic dye-sensitized solar cells. , 2010, The journal of physical chemistry. B.

[29]  N. Koide,et al.  Effects of 4-tert-Butylpyridine and Li Ions on Photoinduced Electron Injection Efficiency in Black-Dye-Sensitized Nanocrystalline TiO2 Films , 2009 .

[30]  Laurence M. Peter,et al.  Characterization of titanium dioxide blocking layers in dye-sensitized nanocrystalline solar cells , 2003 .

[31]  Y. Wada,et al.  Stepped light-induced transient measurements of photocurrent and voltage in dye-sensitized solar cells: application for highly viscous electrolyte systems. , 2005, Langmuir : the ACS journal of surfaces and colloids.

[32]  Hongxia Wang,et al.  A comparison of different methods to determine the electron diffusion length in dye-sensitized solar cells , 2009 .

[33]  Kazuhiro Sayama,et al.  Effect of Cations on the Interactions of Ru Dye and Iodides in Dye-Sensitized Solar Cells: A Density Functional Theory Study , 2011 .

[34]  Y. Wada,et al.  Retardation of interfacial charge recombination by addition of quaternary ammonium cation and its application to low temperature processed dye-sensitized solar cells , 2006, Photochemical & photobiological sciences : Official journal of the European Photochemistry Association and the European Society for Photobiology.

[35]  T. Kitamura,et al.  Influence of the electrolytes on electron transport in mesoporous TiO2-Electrolyte systems , 2002 .

[36]  G. Oskam,et al.  Electron Diffusion and Back Reaction in Dye-Sensitized Solar Cells: The Effect of Nonlinear Recombination Kinetics , 2010 .

[37]  Emilio Palomares,et al.  Charge separation versus recombination in dye-sensitized nanocrystalline solar cells: the minimization of kinetic redundancy. , 2005, Journal of the American Chemical Society.

[38]  Donald Fitzmaurice,et al.  Spectroscopic determination of flatband potentials for polycrystalline TiO2 electrodes in mixed solvent systems , 1994 .

[39]  Laurence M. Peter,et al.  Dynamic Response of Dye-Sensitized Nanocrystalline Solar Cells: Characterization by Intensity-Modulated Photocurrent Spectroscopy , 1997 .

[40]  Hongxia Wang,et al.  Characterization of electron trapping in dye-sensitized solar cells by near-IR transmittance measurements , 2009 .

[41]  F. Fabregat‐Santiago,et al.  Electron Lifetime in Dye-Sensitized Solar Cells: Theory and Interpretation of Measurements , 2009 .

[42]  Anders Hagfeldt,et al.  Investigation of influence of redox species on the interfacial energetics of a dye-sensitized nanoporous TiO2 solar cell , 1998 .

[43]  U. Würfel,et al.  Direct measurement of the internal electron quasi-Fermi level in dye sensitized solar cells using a titanium secondary electrode. , 2006, The journal of physical chemistry. B.