Measured binding coefficients for iodine and ruthenium dyes; implications for recombination in dye sensitised solar cells.
We have measured the binding coefficients of iodine to three dyes used in Dye Sensitised Solar Cells (DSSCs). Binding coefficients are quantified via the effect of iodine binding on the UV-vis spectrum of the dye. From iodine titration curves of dye sensitised TiO(2) films we find that the binding coefficients of iodine to the dyes C101, N719 and AR24 (vide infra) are in the range of 2000-4000 M(-1). From FTIR results and molecular modelling we show the iodine binds to the thiocyanate group in all these dyes. For the AR24 dye we present evidence that iodine also binds to the amine moiety on this dye. With these binding coefficients we show that the dye-iodine complex will be present at much higher concentrations than free iodine in the pore structure of a DSSC. As we have recently shown that iodine (rather than tri-iodide) is the dominant acceptor in electron recombination, the concentration dye-iodine complexes could influence recombination rates and thus V(oc). By comparison of recombination data on full cells, we show that AR24 accelerates recombination by a factor of 7 over N719, presumably due to the iodine binding to the amine group. We leave open the question why iodine binding to the amine group seems to have a stronger effect on the recombination than does binding to the thiocyanate.
Department of Chemistry, Imperial College London, Exhibition Road, London SW7 2AZ, UK.
Xiaoe
X
Li
Anna
A
Reynal
Piers
P
Barnes
Robin
R
Humphry-Baker
Shaik Mohammed
SM
Zakeeruddin
Filippo
F
De Angelis
Brian C
BC
O'Regan
D000537:Aluminum Oxide / Q000737:chemistry; D001665:Binding Sites; D011211:Electric Power Supplies; D005456:Fluorescent Dyes / Q000737:chemistry*; D007455:Iodine / Q000737:chemistry*; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000737:chemistry*; D012428:Ruthenium / Q000737:chemistry*; D012993:Solar Energy; D013056:Spectrophotometry, Ultraviolet; D017550:Spectroscopy, Fourier Transform Infrared; D013861:Thiocyanates / Q000737:chemistry; D014025:Titanium / Q000737:chemistry
D005456:Fluorescent Dyes; D009942:Organometallic Compounds; D013861:Thiocyanates; C506095:bis(2,2'-bipyridyl-4,4'-dicarboxylate)ruthenium(II) bis(tetrabutylammonium) bis(thiocyanate); C009495:titanium dioxide; D012428:Ruthenium; D007455:Iodine; D014025:Titanium; D000537:Aluminum Oxide