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)

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

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

Solar Cell Possibilities $$$$$$ $$ http://en.wikipedia.org/wiki/File:PVeff(rev110707)d.png

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: 400-700 nm 1.8- 3.1 eV 3 Ru2+ → Ru3+ + e− Anode (oxi): 3I−→I−3 +2e− Cathode (red): I−3 +2e−→3I− 1. O’Regan et al. Nature . 1991. 2. Nazeeruddin et al. J.Am.Chem.Soc. 2001. 3. http://bouman.chem.georgetown.edu/S02/lect23/Solar_Spectrum.png\ 4. Grätzel et al. MRS Bulletin. 2005. 5

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 0.0017 mol% 1. Grätzel et al. MRS Bulletin. 2005. 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

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

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. 2008.

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 0.3 1 Teoh et al. Catalysis Today. 2007.

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 http://en.wikipedia.org/wiki/Methylene_blue Height et al. Applied Catalysis B. 2005.

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

Nb-TiO2 Bandgap and Rutile % Nb2O5 Eg = 3.4 eV 0.03 mol% Nb 0.3 1 Teleki et al. Sensor. Actuator. B. 2007 Salvador et al. Solar Energy Materials. 1980.

UV-Photocatalytic Testing Nb-TiO2

Nb-TiO2 Outperforms TiO2

Ru-TiO2 Bandgap and Rutile % Ru02 Eg = 2.4 eV 0.03 mol% Ru 0.3 1 Gujar et al. Electrochemistry Communications. 2007.

UV-Photocatalytic Testing Ru-TiO2

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).

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. 2007.

Future Work Synthesis of DSSC with best catalyst.

Appendix Bandgap Calculations Photocatalytic Process

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

Fe-TiO2 Fe3+ ionic radius: 0.55 Å Ti4+ ionic radius is: 0.67 Å Wikipedia Anatase Rutile 0.03 mol% Fe 0.3 1

Nb-TiO2 Nb5+ ionic radius: 0.64 Å Ti4+ ionic radius is: 0.68 Å Wikipedia Anatase Rutile 0.03 mol% Nb 0.3 1

Ru-TiO2 Fe3+ ionic radius: 0.57.5 Å Ti4+ ionic radius is: 0.67 Å Wikipedia Anatase Rutile 0.03 mol% Ru 0.3 1

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 -300-400 nm -5 ppm oxalic acid -1 kg(catalyst)/m3 -FSP -λ > 400 nm -10 oxalic acid Teoh et al. Catalysis Today. 2007. Li et al. J. Hazardous Materias. 2008 Navío et al. Journal of Molecular Catalysis A. 1996.

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

Bandgap Calculations Fe

Bandgap Calculations Nb

Bandgap Calculations Ru

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