Thiocyanate ligand substitution kinetics of the solar cell dye Z-907 by 3-methoxypropionitrile and 4-tert-butylpyridine at elevated temperatures

Nguyen Tuyet Phuong, Rikke Degn, Thai Hoang Nguyen, Torben Lund

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The dye sensitized solar cell dye Z-907, [RuLL´(NCS)2] may loose a thiocyanate ligand at elevated temperatures (80-100 ºC) by ligand exchange with the solar cell additive 4-tert-butylpyridine

(4-TBP) or the electrolyte solvent 3-methoxypropionitrile (3-MPN). The mechanism in homogeneous solution proceeds via three equilibrium reactions (eqs. 1-3) with the solvent complex [RuLL´(NCS)(3-MPN)] as an intermediate:


[RuLL´(NCS)2] + 3-MPN = [RuLL´(NCS)(3-MPN)]+ + NCS- (1)

[RuLL´(NCS)(3-MPN)]+ + 4-TBP = [RuLL´(NCS)(4-TBP)]+ + 3-MPN (2)

[RuLL´(NCS)2] + 4-TBP = [RuLL´(NCS)(4-TBP)]+ + NCS- (3)



A similar mechanism describes the heterogeneous substitution reactions of Z-907 attached to the surface of TiO2 particles with 3-MPN and 4-TBP. All the six homogeneous and heterogeneous rate constants were obtained at 100 ºC by monitoring the decay of Z-907 and product formation in test tube experiments by HPLC coupled to UV/Vis and electrospray mass spectrometry.

A half life time t1/2 = 150 h was obtained for the Z-907 dye bound to TiO2 nano crystalline particles at 85 ºC in presence of 4-TBP and 3-MPN. Dye sensitized solar cells (DSC) with Z-907 as sensitizer and application of the so called “non robust” electrolytes containing 4-TBP and 3-MPN is therefore not expected to be able to pass a 1000 h thermal stress test at 85 ºC. Addition of thiocyanate to the cell electrolyte may however, eliminate or reduce the problems caused by dye thiocyanate ligand substitution in DSC cells.

TidsskriftSolar Energy Materials & Solar Cells
Udgave nummer11
Sider (fra-til)1939-1945
Antal sider7
StatusUdgivet - 2009


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