Abstract
Long, well-separated single crystal TiO2 nanowire (NW) arrays with rapid charge transport properties hold great promise in photoelectrochemical and energy storage devices. Synthesis variations to increase the NWs length generally result in the widening of the NWs and fusion at their roots which, in turn, increases the structural disorder and slows charge transport. As such, well-separated single-crystal TiO2 NW arrays with rapid charge transport properties have been limited to lengths of about 3-4 μm. In this work, by adjusting the HCl/DI-water ratio and adding specific organic ligands to the reaction solution that slow the lateral growth rate we achieve well-separated single-crystal rutile TiO2 NW arrays with a length of ∼10 μm and an aspect ratio of approximately 100. The charge transport is 100 times faster than that of nanoparticle films and remarkably exhibits length-independence, a behavior that can be attributed to the well-separated architecture. The synthesis strategy can be extended to the fabrication of other well-separated metal oxide NW arrays and represents an important tool in achieving high performance photoelectrochemical and electrical energy storage devices.
Highlights
Recent work on well-separated singlecrystal rutile TiO2 NW arrays has shown that the electron diffusion coefficient is two orders of magnitude higher than that in mesoporous lms comprised of randomly packed nanoparticles (NPs), corresponding to an electron diffusion length of about 60 mm[9] and offering the promise of useful application of long NW arrays within devices such as solar cells, photodetectors, and chemical sensors.[10,11,12,13]
This, in turn, reduces the aspect ratio, increases the structural disorder and reduces the charge transport;[19,20] experimental results shown in Electronic supplementary information (ESI) Fig. S1† indicate that the diffusion coefficient of bundled TiO2 NWs is over one order of magnitude lower than that of wellseparated ones
A FTO coated glass substrate supporting a TiO2 seed layer was loaded into a Te on-lined stainless-steel reactor (23 mL) lled with a reaction solution composed of 2butanone, ethanol, hydrochloric acid (HCl, 37%) and titanium butoxide (TBOT)
Summary
Aligned semiconductor nanowire (NW) arrays have attracted great attention due to their unique optical and electronic properties.[1,2,3,4,5,6,7,8] Recent work on well-separated singlecrystal rutile TiO2 NW arrays has shown that the electron diffusion coefficient is two orders of magnitude higher than that in mesoporous lms comprised of randomly packed nanoparticles (NPs), corresponding to an electron diffusion length of about 60 mm[9] and offering the promise of useful application of long NW arrays within devices such as solar cells, photodetectors, and chemical sensors.[10,11,12,13] the synthesis of well-separated rutile TiO2 NW arrays has been limited to lengths of about 3–4 mm.[7,14,15] During the conventional bottom-up growth process, synthesis variations to increase the length generally result in the widening of the NWs and subsequent fusion at their roots.[16,17,18] This, in turn, reduces the aspect ratio, increases the structural disorder and reduces the charge transport;[19,20] experimental results shown in ESI Fig. S1† indicate that the diffusion coefficient of bundled TiO2 NWs is over one order of magnitude lower than that of wellseparated ones.
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