Document Type

Thesis - University Access Only

Award Date

2011

Degree Name

Doctor of Philosophy (PhD)

Department / School

Electrical Engineering and Computer Science

Abstract

Photovoltaic technology has attracted much of attention in the field of renewable energy resources to fulfill the increasing energy demand, due to its affordable cost, cleanliness and easy maintenance compared to other renewable energy technologies. DSSCs use low cost materials and simple fabrication techniques thus it can be a potential alternatives to silicon based photovoltaic technology. Performance of DSSCs is limited by electron recombination at the interfaces. RF-sputtered TiO 2 compact layers were grown on ITO surface used as a compact layer in DSSC which was compared to a DSSC with sol-gel processed TiO2 compact layer. The DSSC with sol-gel processed TiO2 compact layer resulted in efficiency of 1.3%. Poor electronic quality of the TiO2/electrolyte interface would explain the poor PV performance of this solar cell. The DSSC with RF-sputtered TiO 2 compact layer resulted in 5.9%. Superior PV characteristics of the DSSC with RF-sputtered TiO 2 compact layer than DSSC with sol-gel TiO2 compact layer, especially a much higher Voc, are in line with the results of dark 1-V measurement and suggest that the electronic quality of the RF-sputtered TiO 2/electrolyte interface was better than the electronic quality of the sol-gel TiO 2/electrolyte interface. Photoconversion efficiency of the DSSCs with AhO 3 compact layer was 5.1% while the DSSC with HfO2 compact layer resulted 6.0 %. In this set of experiments, the DSSC with conventional sol-gel processed TiO2 compact layer resulted in efficiency of 3.6%. Photoconversion efficiency of the DSSC with HfO2 compact layer was improved 66 % (3.6 to 6 %) compared to the DSSC with sol-gel TiO2. In case of A12O3, the enhancement was about 41 %. (3.6 to 5.1). Voe decay and EIS measurements suggested that electron life time was significantly improved in the DSSCs with ALD grown compact layers compared to sol-gel TiO2 compact layer. AhO 3 and HfO2 interfacial layers, grown by ALD, were used to treat mesoporous TiO2 surface. AFM images suggested that ALD grown metal oxides did not block the porosity in TiO2 film and hence no significant effect on dye loading. DSSCs with AhO 3 interfacial layer resulted in 5 % efficiency while the DSSCs with HfO2 showed 7.1 %. In case of DSSC with no interfacial layer, activation energy of charge transport was 1.03 e V while the DSSC with AhO 3 showed 1.27 e V and the DSSC with HfO 2 showed 1.31 eV. It confirmed the defect density and activity at the TiO2/electrolyte interface was engineered by interfacial layers. Further, DSSCs with interfacial layers resulted in higher 11 than that of DSSC with no interfacial layer. This can be attributed to the enhancement in electron life time at the Ee of conduction band due to reduced probability of electron capture by Ti 0 2 surface states at the bandgap and consecutive recombination with a hole at either dye or electrolyte. The significant enhancement observed in Jsc and Tl of the DSSCs with interfacial layers.

Library of Congress Subject Headings

Dye-sensitized solar cells

Photovoltaic power generation

Interfaces (Physical sciences)

Format

application/pdf

Number of Pages

237

Publisher

South Dakota State University

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