1. The Effect of Dopants on TiO2 Solar Cell Efficiency Mini Project Presentation FS09
E. Buitrago
Advisors: Dr. A. Teleki and A. Tricoli
Particle Technology Laboratory
Swiss Federal Institute of Technology (ETHZ)

2. Overview Introduction Global energy problem Solar Cell possibilities
Dye Sensitized Solar Cells
Narrowing the TiO2 bandgap: doping
Experimental
FSP particle synthesis
Photocatalytic Experiments
Bandgap Calculations
Results Fe Nb Ru
Conclusion
Outlook
Future Work

3. World Energy Use http://www.flickr.com/photos/33264427@N06/3166865015/

4. Solar Cell Possibilities
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5. Dye Sensitized Solar Cell (DSSC) Schematic
A.R. U. Absorbance
Anode (-) 2
Cathode (+) 1
I- / I-3
Wide bandgap semiconductor
Eg = 3.2 eV ~ 385 nm (4)
Visible light: nm eV 3
Ru2+ → Ru3+ + e−
Anode (oxi): 3I−→I−3 +2e−
Cathode (red): I−3 +2e−→3I−
1. O’Regan et al. Nature
2. Nazeeruddin et al. J.Am.Chem.Soc 3.
4. Grätzel et al. MRS Bulletin 5

6. Maximizing Visible Light Absorption: Dopants
Bandgap
Method
Concentration
1. TiO2
3.2 eV (anatase)
2. Fe-TiO2
2.2 eV
FSP
30 mol%
Solubility limit 5 mol%
3. Ru-TiO2
2.56 eV
Ion exchange
0.018 mol%
4. Nb-TiO2
2.9 eV
Sol gel
mol%
1. Grätzel et al. MRS Bulletin
2.Teoh et al. Catalysis Today. 2007
3. Khan et al. Appl. Surf. Sci. 2009
4. Salvador et al. Solar Energy Materials. 1980
0.03, 0.3, 1 mol% dopant

7. FSP Particle Synthesis
TiO2:
0.5 M TTIP in Xylene/Acetronile(3:1)
Dopant Precursors :
Fe: Iron Acetylacetonate
Nb: Niobium 2-Ethylhexaonate
Ru: Ruthenium (III) Acetylacetonate
5/5 Flame d
Mädler et al. J. Aerosol Sci. 2002

8. Bandgap Calculations
UV-vis Spectrometry
Indirect Semiconductor hvα = const (hv-Eg)2 hv = energy of incident photon [eV] α = absorption coefficient [cm-1] α = A/l A = Absorbance (measured with UV-vis) l = cuvette length
Singh et al. International Journal of Hydrogen Energy

9. Fe-TiO2 Bandgap and Rutile %
Teoh et al.
mol %
Eg [eV]
Rutile %
3.2 15
0.5
3.13 18 2
2.9 32
0.03 mol% Fe
Teoh et al. Catalysis Today

10. Photocatalytic Experiments with UV-Light
10 ppm Methylene Blue
8 W
UV –lamp
366 nm
Catalyst loading:
0.3 kg/m3
UV –Vis 665 nm
Height et al. Applied Catalysis B

11. UV-Photocatalytic Testing Fe-TiO2
-0.5 kg(catalyst)/m3
-Hydrothermal doping
-366 nm
-100 ppm MB

12. Nb-TiO2 Bandgap and Rutile %
Nb2O5 Eg = 3.4 eV
0.03 mol% Nb
Teleki et al. Sensor. Actuator. B. 2007
Salvador et al. Solar Energy Materials

13. UV-Photocatalytic Testing Nb-TiO2

14. Nb-TiO2 Outperforms TiO2

15. Ru-TiO2 Bandgap and Rutile %
Ru02 Eg = 2.4 eV
0.03 mol% Ru
Gujar et al. Electrochemistry Communications

16. UV-Photocatalytic Testing Ru-TiO2

17. Conclusion TiO2 Bandgap reduced by FSP with Nb and Fe.
Highest bandgap reduction Fe- 1 mol%.
Highest photocatalytic activity under UV light for Nb-TiO2 at 0.3 mol% by (2.95 eV).

18. Outlook
Investigation of photocatalytic activity under visible light for Fe.
= 5 mol%
-1 kg(catalyst)/m3
-FSP
-λ > 400 nm
-10 oxalic acid
Teoh et al. Catalysis Today

19. Future Work
Synthesis of DSSC with best catalyst.

20. Appendix
Bandgap Calculations
Photocatalytic Process

21. Photocatalytic Process
Photo-generation of electron/hole pair
Formation of radicals (Ox)
Radical oxidation of organic compound
Kim et al. Catalysis Letters. 2007

22. Fe-TiO2 Fe3+ ionic radius: 0.55 Å Ti4+ ionic radius is: 0.67 Å
Wikipedia
Anatase
Rutile
0.03 mol% Fe

23. Nb-TiO2 Nb5+ ionic radius: 0.64 Å Ti4+ ionic radius is: 0.68 Å
Wikipedia
Anatase
Rutile
0.03 mol% Nb

24. Ru-TiO2 Fe3+ ionic radius: 0.57.5 Å Ti4+ ionic radius is: 0.67 Å
Wikipedia
Anatase
Rutile
0.03 mol% Ru

25. Photocatalytic Testing with MB
0.004 mol%
0.04 mol%
= 5 mol%
-1 kg(catalyst)/m3
-Impregnation method
n: Fe(NO3)3•9H2O
a: Iron acetylacetonate complex
-λ > 400 nm
-5 ppm oxalic acid
-0.5 kg(catalyst)/m3
-Hydrothermal doping
-366 nm
-100 ppm MB
-0.5 kg(catalyst)/m3
-Impregnation method
n: Fe(NO3)3•9H2O
a: Iron acetylacetonate complex nm
-5 ppm oxalic acid
-1 kg(catalyst)/m3
-FSP
-λ > 400 nm
-10 oxalic acid
Teoh et al. Catalysis Today
Li et al. J. Hazardous Materias. 2008
Navío et al. Journal of Molecular Catalysis A

27. Bandgap Calculations
Indirect Semiconductor hvα = const (hv-Eg)2 hv = energy of incident photon [eV] α = absorption coefficient [cm-1] α = A/l A = Absorbance (measured with UV-vis) l = cuvette length

28. Bandgap Calculations Fe

29. Bandgap Calculations Nb

30. Bandgap Calculations Ru

31. TiO2 Bond Orbitals Conduction Band Ti d + (O2p) O2P + ( Ti d)
Energy
TiO2 Bond
Orbitals
Conduction Band
Ti d + (O2p)
Ti d
Eg = 3.2 eV
O2p
O2P + (
Ti d)
Valence Band