## 2 Results and Discussion  
SANP-S was synthesised by a new and facile one-step solvothermal process, as reported elsewhere [26]. Briefly, titanium isopropoxide (TTIP, Sigma, USA) (1.5 mL) was added dropwise to an acetic acid (Sigma, USA)-ethanol (Chem-Supply, Australia) mixed solvent (1:2 v/v) under vigorous stirring for (1 h) at room temperature. A transparent solution was formed, which was then transferred into a 45 mL Teflon-lined stainless steel autoclave (Parr Instrument Company, USA) and heated to 200 \({}^{\circ}\)C (ramp time of 1 \({}^{\circ}\)C /min) for 9 h. After cooling down to room temperature, the resulting white precipitate was collected and washed with distilled water and ethanol three times. The material for SANP-S was then dried overnight at 90 \({}^{\circ}\)C and calcined at 500 \({}^{\circ}\)C (ramp time of 1 \({}^{\circ}\)C /min) in the air for three hours. This was then redispersed in ethanol, while SANP-T was maintained in ethanol. The dispersions were combined with terpineol (Alfa Aesar, USA) and ethyl cellulose (Sigma, USA) to create pastes similar to those in our previous reports [15; 18; 27]. These pastes were then screen-printed onto substrates and calcined following a multi-step program up to 500 \({}^{\circ}\)C.  
The X-ray diffraction (XRD) patterns in Figure 1a show that the samples collected from printed films of SANP-S and SANP-T were both phase-pure and well-crystallised anatase TiO\({}_{2}\) (SPD.21-1272), with crystallite sizes of around 25 nm. The SANP-S sample showed slightly narrower peaks, implying slightly higher crystallinity due to the additional sintering time. Previously, we demonstrated the role amorphous content plays on DSC performance, as a result of decreased charge injection efficiency [18]. Preliminary measurements showed the amorphous content to be quite low in these materials (only a few percent at most; data to be published elsewhere [26]), indicating that this would not be a major factor affecting the charge injection efficiency. Raman spectra of SANP-S and SANP-T (Figure 1b) also showed both materials to be anatase TiO\({}_{2}\), confirmed by six characteristic Raman vibrational modes centered at 144 cm\({}^{-1}\) (E\({}_{\text{g}\,(1)}\)), 197 cm\({}^{-1}\) (E\({}_{\text{g}\,(2)}\)), 399 cm\({}^{-1}\) (B\({}_{\text{lg}}\)), 513 cm\({}^{-1}\) (A\({}_{\text{lg}}\)), 519 cm\({}^{-1}\) (B\({}_{\text{lg}}\)), and 639 cm\({}^{-1}\) (E\({}_{\text{g}\,(3)}\)), respectively [28]. The slightly higher intensity (less broadening) of peaks in SANP-S again indicates better crystallinity compared to SANP-T. The low- and high-magnification scanning electron microscope (SEM) images (Figure 2a-d) show the morphologies of SANP-S and SANP-T films. It can be observed that SANP-S (Figure 2a,b) had a more aggregated structure and non-uniform surface topography compared to SANP-T (Figure 2c,d), in line with our expectations. SANP-S films also showed significant cracking at this scale, which  
Figure 1: (a) X-ray diffraction patterns of powder collected from scratched SANP-S and SANP-T films; (b) Raman spectra of SANP-S and SANP-T films. is attributed to aggregation. Both had similar particle size about 25 \(\pm\) 3 nm, in line with the above XRD results. Figure 3a,b show the specific surface area and the pore size distributions in the two structures. The type (IV) nitrogen adsorption/desorption isotherm branches indicate that both materials have mesoporous structure [29; 30] with similar porosities of \(\sim\)64% (Figure 3a). [27] On the other hand, SANP-T has a more uniform pore size distribution, with a broader range of pores in the 2-30 nm range. SANP-S also revealed some larger pores, as shown in Figure 3b, which were attributed to the cracked structure seen in SEM images above and in (Figure S1, Supplementary Materials). The SANP-S also has a slightly lower surface area (113 m\({}^{2}\cdot\)g\({}^{-1}\)) compared to SANP-T (119 m\({}^{2}\cdot\)g\({}^{-1}\)), which could be attributed to aggregation, and is in line with our previous experimental results for similar systems [15].