Mesoporous TiO2 single crystals delivering enhanced mobility and optoelectronic device performance



Mesoporous ceramics and semiconductors enable low-cost solar power, solar fuel, (photo)catalyst and electrical energy storage technologies1. State-of-the-art, printable high-surface-area electrodes are fabricated from thermally sintered pre-formed nanocrystals2,3,4,5. Mesoporosity provides the desired highly accessible surfaces but many applications also demand long-range electronic connectivity and structural coherence6. A mesoporous single-crystal (MSC) semiconductor can meet both criteria. Here we demonstrate a general synthetic method of growing semiconductor MSCs of anatase TiO2 based on seeded nucleation and growth inside a mesoporous template immersed in a dilute reaction solution. We show that both isolated MSCs and ensembles incorporated into films have substantially higher conductivities and electron mobilities than does nanocrystalline TiO2. Conventional nanocrystals, unlike MSCs, require in-film thermal sintering to reinforce electronic contact between particles, thus increasing fabrication cost, limiting the use of flexible substrates and precluding, for instance, multijunction solar cell processing. Using MSC films processed entirely below 150 °C, we have fabricated all-solid-state, low-temperature sensitized solar cells that have 7.3 per cent efficiency, the highest efficiency yet reported. These high-surface-area anatase single crystals will find application in many different technologies, and this generic synthetic strategy extends the possibility of mesoporous single-crystal growth to a range of functional ceramics and semiconductors.

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Figure 1: MSC synthesis of TiO2.
Figure 2: X-ray and electron diffraction of mesoporous TiO 2 crystals.
Figure 3: MSC size control via nucleation seed density.
Figure 4: Electronic properties and device performance of MSCs.


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This work was funded by the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement number 246124 of the SANS project, the European Research Council (HYPER project number 279881), the Rhodes Trust, the Engineering and Physical Sciences Research Council, and the Government of the Republic of Trinidad and Tobago. We thank C. Ducati for help with indexing of electron diffraction patterns.

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E.J.W.C. and H.J.S. conceived the idea of the project. E.J.W.C. devised and performed materials synthesis and characterization. N.N. and V.S. fabricated and characterized solar cells and optoelectronic devices. T.L. and J.A.A.-W. contributed to electronic mobility measurements. E.J.W.C., H.J.S. and V.S. wrote the manuscript. All authors commented on the manuscript. H.J.S. supervised the project.

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Correspondence to Henry J. Snaith.

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The authors declare no competing financial interests.

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Crossland, E., Noel, N., Sivaram, V. et al. Mesoporous TiO2 single crystals delivering enhanced mobility and optoelectronic device performance. Nature 495, 215–219 (2013).

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