Aqueous Solution Synthesis of Crystalline Anatase Nanocolloids for the Fabrication of DSC Photoanodes

Abstract

The production of anatase nanocolloids via a novel aqueous solution synthesis method is described. The process involves forced hydrolysis of 0.2 M TiCl 4 aqueous solution at low temperature ͑80°C͒ leading to fast nucleation of TiO 2 anatase nanoparticles ͑4-5 nm͒. The isolated nanopowders were found to consist predominantly of anatase as the major phase ͑ ϳ 85 wt %͒, possess a very high surface area ͑up to 250-350 m 2 /g͒, and a relatively elevated surface hydroxyl content in comparison with the P25 reference material. Single-layer ͑ϳ12 m thick͒ photoanodes prepared with aqueous-synthesized powders were found to have a specific surface area of ϳ130 m 2 /g and the anatase nanocrystallites to have grown to ϳ12 nm and assume a higher degree of crystallinity but still carry ϳ1.5% surface OH groups. The pore size of the film was determined to be ϳ8 nm. By comparison, the film prepared with P25 nanoparticles had the following properties: 50 m 2 /g, 30 nm crystallite size, 0.2% surface OH, and 25 nm pore size. Dye-sensitized solar cell ͑DSC͒ devices assembled with the newly fabricated photoanodes showed equivalent photoelectrochemical performance ͓power conversion efficiency , short-circuit current voltage I sc , open-circuit voltage V oc , and Fill Factor ͑FF͔͒ to cells prepared using the benchmark P25 titania powder.The synthesis of nanostructured TiO 2 powders for the fabrication of mesoporous photoanodes in dye-sensitized solar cells ͑DSCs͒ has been widely investigated in the last decade. 1 The light-to-current conversion yield of such device is known to depend on a number of parameters, including the properties of the TiO 2 powder material used for the fabrication of the photoanode. Among these properties, particle size and morphology, 2-4 crystallinity, phase content, 5,6 bandgap, 4 chemical composition ͑doping͒, 7 and surface groups 8,9 have been extensively studied and shown to have a significant bearing on the overall efficiency of the DSC devices.Different methods have been developed for the synthesis of TiO 2 particles with properties suited for the fabrication of photoanodes. Among these is the two step sol-gel/hydrothermal synthesis process: 10-12 a titanium alkoxide-based solution ͑usually titanium tetraisopropoxide or butoxide in ethanol͒ is first hydrolyzed to form amorphous TiO 2 powders; crystallization is then induced in an autoclave at high pressure and temperature ͑typically 250°C͒. This method has been successfully developed for the preparation of anatase TiO 2 nanoparticles ͑10-30 nm͒ with large surface area ͑80-150 m 2 /g͒. 13 However, sol-gel processing, especially some complex variations of it, 14 is chemical and energy intensive, multistep, and time-consuming and so does not lend itself to easy scale-up and cost-effective operation. The P25 TiO 2 powder from Degussa ͑20% rutile, 80% anatase, 50 m 2 /g, 30 nm average particle size͒, which is considered a reference material among the commercially available nanostructured TiO 2 powders, is produced by flame synthesis. 15 This process, although ef...

Facile self-assembly and stabilization of metal oxide nanoparticles

“…The 3-5 nm TiO 2 NPs nanoparticles were produced by low temperature (80°C, 30 min) hydrolysis of a 0.125 M TiCl 4 ÁTHF precursor using a method adapted from previous work [30]. To prepare a typical mixed colloid, first an aqueous suspension of P25 (8 wt% in water) was prepared and sonicated for 30 min.…”

“…The second type of TiO 2 nanoparticles (TiO 2 NPs) consists mostly of anatase nanocrystals (3-5 nm) and a very small fraction of rutile nano-needles [30] (ESI Fig. 1).…”

Thin single screen-printed bifunctional titania layer photoanodes for high performing DSSCs via a novel hybrid paste formulation and process

“…For example, crystallite size and morphology, [9][10][11] crystallinity, 12 phase content, 13 doping, 14,15 and surface groups 16 have been shown to have a significant bearing on the overall efficiency of DSSC devices. Recently, our group reported on aqueous-synthesized anatase nanocolloids 17 possessing very high specific surface area and rich hydroxyl content, properties that were shown to lead via optimized dye (N719) anchoring/coating 18,19 to longer electron lifetime. 16 The films made from this new crop of anatase nanocolloids suffered, however, from small pore size distribution leading to electrolyte diffusion resistance and loss of photocurrent output and efficiency.…”

“…It is one of the goals of this paper to report on a new rutile particle variety synthesized via controlled forced hydrolysis 20 that consists of "urchin"-like nanofibrestructured (200-400 nm) particles that proved superior scattering centers in hybrid formulation with our aqueoussynthesized anatase (5-10 nm). 17 Furthermore, we report the optimization of the hybrid paste via the incorporation of P25 nanoparticles that we show via physical and electrochemical characterizations to eliminate losses due to electrolyte diffusion resistance or interfacial charge recombination. Last but not least, it is demonstrated that DSSCs incorporating single-layer screen-printed films of only 5-6 lm in thickness can be built with the novel hybrid paste that compete favorably with double thickness photoanodes based on benchmark commercial paste material.…”

Vibrational Spectroscopic Imaging of N719-TiO2 Films in the High Wavenumber Region Coupled to EIS Analysis

“…This is done to reveal the role of surface groups before and after adsorption of two different TiO 2 films; one is a commercial product ("Dyesol") and one made from a hydroxyl-rich anatase variety ("Aqueous") synthesized in our laboratory. 23,24 The influence of these surface binding features on the photovoltaic performance of DSSC devices prepared with the two different TiO 2 electrodes is also discussed on the basis of electrochemical impedance spectroscopic analysis and I-V curve measurements.…”