Date of Award

12-2013

Degree Type

Thesis

Degree Name

Engineering (M.S.E.)

Department

School of Engineering

First Advisor

Heidi Jiao

Second Advisor

Nael Barakat

Third Advisor

Bruce Dunne

Abstract

Dye Sensitized Solar Cells (DSSC) offer advantages over semiconductor solar cells including lower costs and relaxed material purity requirements. However, DSSC solar energy conversion efficiencies are lower than many competing photovoltaic technologies. Key to DSSC performance is the incorporation of nanocrystalline metal oxides to provide a large surface area for photosensitive dye loading. Titanium dioxide (TiO2) is the predominately used metal oxide. The structure of the TiO2 layer determines charge transfer efficiency and the level of generated photocurrent. Common practice for high performance cells is to deposit a thin, compact TiO2 coating followed by a thicker, more porous TiO2 layer. Often, different deposition methods are used for each layer.

Inkjet printing of TiO2 potentially offers a high degree of control over the deposition of TiO2 suspensions. Previous use of inkjet printing for TiO2 depositions have focused on producing TiO2 films with uniform density. A multi-ink printing system offers the possibility of forming TiO2 films with variable density using a single deposition method.

For this research, inkjet printing of TiO2 films with a graded density profile was explored as a means of improving DSSC performance. Cell performance was assessed through the measurement of generated currents and device Fill Factors.

Two means to produce density variations in TiO2 layers were explored: TiO2 particle size and layer pore-volume. For the former, the reduction of micron-sized TiO2 particles using a milling approach was attempted but proved unsuccessful. To affect changes in pore-volume, several TiO2 suspensions were developed with varying pore-forming content that successfully produced variations in layer density. DSSCs with printed TiO2films having three density layers showed an average improvement in the Fill Factor of 8% versus single layers and 6% versus double layers. Short-circuit currents in tri-layer films increased an average of 35% over single layers and 13% over double layers.

The results effectively demonstrated the potential for using inkjet printing as a sole deposition method to produce TiO2 films with a non-uniform density leading to improved DSSC performance. One possibility for further study would be to create further layer variations through the simultaneous printing of different suspensions.

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