Year

2015

Degree Name

Doctor of Philosophy

Department

Institute for Superconducting and Electronic Materials

Abstract

Solar energy is the largest source of carbon-free energy that can be converted into heat and electricity. Since the early 1990s, dye-sensitized solar cells (DSCs) have received a great deal of attention as a promising alternative photovoltaic technology on account of their projected low costs and reduced energy input in manufacture. Considerable efforts have been made to improve the energy conversion efficiency, by developing or modifying DSC components, such as sensitizers, photoanodes, electrolytes, and counter electrodes. However, a number of challenging issues remain, such as new optimised structures are required as DSCs evolve. The aims of this thesis are to design, develop and investigate new semiconductor TiO2 architectures for use as photoanodes in different types of DSC (such as flexible DSCs, cobalt-based DSCs, rutile TiO2-based DSCs) applications.

Among the novel materials developed as part of this thesis, a new type of highly connected hierarchical textured TiO2 spheres (HCHT) was rationally designed for DSCs. An overall energy conversion efficiency of up to 9.0 % can be achieved by using these HCHT as the photoelectrode with N719 dye, a considerable improvement over state-of-the-art commercial available TiO2 particles (Dyesol TiO2 paste) (8.2 %) under the same conditions.

A new photoanode architecture for cold isostatic pressing (CIP), with a new mesoporous hierarchical anatase TiO2 (MHAT) architecture deposited onto P25, was rationally designed for efficient charge transport and better light management in flexible dye-sensitized solar cells, with a 5.6 % conversion efficiency realized.

Mesoporous anatase single crystals (MASCs) with special polyhedral pores (~ 7 nm) is employed to construct MK-2–sensitized solar cells using a cobalt redox shuttle, with a maximum efficiency of 8.7 % achieved, which is significantly higher than for analogous devices based on commercial Dyesol TiO2 (6.3 %).

A DSC combining a well-defined 3D hierarchical rutile TiO2 architecture (HRT) is reported in conjunction with a high-extinction-coefficient metal-free organic sensitizer (D149), achieving a conversion efficiency of 5.5 %, which is superior to ones employing P25 (4.5 %), comparable to state-of-the-art commercial transparent titania anatase paste (5.8 %). Further to this, an overall conversion efficiency 8.6 % was achieved when HRT was used as the light scattering layer, a considerable improvement over the commercial transparent/reflector titania anatase paste (7.6 %), a significantly smaller gap in performance than has been seen previously. In addition, two dyes, N719 and D149, were used as sensitizers of the modified HRT-based DSCs, with maximum η of 5.6 % and 5.8 % achieved, respectively.

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