Rapid extraction of photogenerated charge carriers is essential to achieve high efficiencies with perovskite solar cells (PSCs). Here, a new mesoscopic architecture as electron‐selective contact for PSCs featuring 40 nm sized TiO2 beads endowed with mesopores of a few nanometer diameters is introduced. The bimodal pore distribution inherent to these films produces a very large contact area of 200 m2 g−1 whose access by the perovskite light absorber is facilitated by the interstitial voids between the particles. Modification of the TiO2 surface by CsBr further strengthens its interaction with the perovskite. As a result, photogenerated electrons are extracted rapidly producing a very high fill factor of close to 80% a VOC of 1.14 V and a PCE up to 21% with negligible hysteresis.
Surface treated macro and nanoparticle TiO 2 samples have been prepared, characterised and their efficiency as UV blockers evaluated in clear coatings and paints. The particle size of the 'base' TiO 2 has been optimised to block UV radiation and the surface treatment developed to deactivate the photocatalytic activity of the surface of the TiO 2 particles. The resultant UV blockers have been evaluated in both solvent and water-based clear coatings. Nanoparticle TiO 2 has been prepared from 'seed' and the particle size was controlled by calcination. It was found that the choice of particle size is a compromise between UVA absorption, UVB absorption, visible transmission and photoactivity. It has been demonstrated that TiO 2 with a crystallite size of 25 nm yields a product with the optimum properties. A range of dispersants was successfully used to disperse and mill the TiO 2. Both organic and inorganic dispersants were used; 2-amino-2-methyl-1-propanol and 1-amino-2-propanol (MIPA) and P 2 O 5 and Na 2 SiO 3 respectively. The surface of the nano-TiO 2 was coated with mixed oxides of silicon, aluminium, zirconium and phosphorous. Addition of the resultant coated nano-rutiles to an Isocyanate Acrylic clear coating prolonged the lifetime of that coating compared to the blank. Generally, a surface treatment based on SiO 2 , Al 2 O 3 and P 2 O 5 was more successful than one based on ZrO 2 , Al 2 O 3 and P 2 O 5. Higher addition levels of the surface treatment were beneficial for protecting the polymeric coating. The UV blocker products were also evaluated in a water-based acrylic, first a water-based dispersion of the UV blocker was prepared before addition to the acrylic. The dispersions and resultant acrylic thin films were evaluated using UV/Vis spectroscopy and durability assessed. The ratio of absorbance at 300:500 nm for the water-based dispersion was shown to be a good predictor of both the transparency of the resultant acrylic thin film and the durability of that film, in terms of weight loss. Macro grade titanium dioxide pigments were also prepared and coated with treatments of silica, alumina and siloxane and their photo-stabilising activity in alkyd paint film assessed and found to be directly related to the electron-hole pair mobility and trapping as determined by microwave spectroscopy.
The ultraviolet–visible (UV–Vis) absorption properties of a range of nano‐particle titanium dioxides have been optimized and interrelated to the effects of the nature of calcination versus wet milling methodologies. Different inorganic and organic surfactants and surface treatments were also assessed. The TiO2 particles as prepared were characterized using X‐Ray diffraction spectrometry (XRD), transmission electron microscopy (TEM), BET, UV/Vis spectroscopy, and CPS disk centrifuge. Data are related to their spectral absorption properties and weathering stability in an isocyanate‐acrylic coating via gloss retention and weight loss. The choice of particle size is a compromise between UVA absorption, UVB absorption, visible transmission, and photoactivity. It is demonstrated that TiO2 with a crystallite size of 25 nm yields a product with the optimum properties. A method using UV/visible absorption spectroscopy has been developed and found to give excellent sensitivity to particle size was shown with CPS (disk centrifuge). It is shown to be a useful way to assess nano‐TiO2 dispersions. The wet milling of the base TiO2 before surface treatment was also optimized utilizing different dispersants. It was shown that using the ratio of absorbance at 300:550 nm is a good approximation for the ratio of the whole area under the curve in the UV spectrum to that in the visible region. This was used as an indication of the generation of smaller fragments generated by milling the larger aggregates. The particle‐size distribution and nature of the wet‐milling process significantly influenced the subsequent accelerated ATLAS weathering performance of the titania particles in an isocyanate‐acrylic coating.
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