Converting solar energy directly into electricity as a clean and renewable energy resource is immensely important to solving the energy crisis and environmental pollution problems induced by the consumption of fossil fuels. Dye-sensitized solar cells (DSSCs) provide a technically and economically credible alternative that could challenge the dominance of conventional p-n junction photovoltaic devices in the solar energy market. DSSCs use dye molecules adsorbed at the surface of nanocrystalline oxide semiconductors such as TiO2 to collect sunlight. These thin films require a large surface area, to adsorb many dye molecules, and mesoporous channels so the electrolyte can permeate the film and regenerate the dye molecules. This favourable morphology is traditionally achieved by the random assembly of a network of nanoparticles by the sintering process.Two-photon polymerization is a 3D printing technique used to fabricate structures with feature resolutions down to 100 nm. We use this technique to fabricate TiO2 thin films of optimised 3D micro-design for use in DSSCs. Our films have a considerable advantage over the conventional (random assembly) films as it allows the implementation of light scattering designs which are shown to significantly enhance photocurrent in the cell by up to ~25%.

Developments in semiconductor science have led to the miniaturization and improvement of light detection technologies for many applications. However, traditional pn-junctions or three-dimensional device geometries for detection of ultraviolet (UV) light are still limited by the physical properties of the semiconductors used, such as the small penetration depth of UV light in silicon. Van der Waals (vdW) semiconductors and their pn-junctions can offer an alternative solution due to their optical properties and thin pn-junction region. Here, we report on a multi-layer junction that combines single layer graphene and vdW semiconductors (p-GaSe and n-In2Se3) with strong optical absorption in the UV range. The junctions have broadband spectral response (0.3-1.0 μm) and high photoresponsivity under forward and reverse bias, or without any externally applied voltage. The photoresponse differs from that of a traditional pn-junction diode as it is governed by charge transport across thin layers and light-current conversion at three vdW interfaces (e.g. the graphene/GaSe, GaSe/In2Se3 and In2Se3/graphene interfaces). The type-II band alignment at the GaSe/In2Se3 interface and electric field at the three vdW interfaces are beneficial to suppress carrier recombination for enhanced photoresponsivity (up to ~102 A/W) and detectivity (up to ~1013 Jones), beyond conventional UV-enhanced silicon detection technology.

Windows integrated with semi-transparent photovoltaics (PVs) such as Dye-Sensitized Solar Cells (DSSCs) show good potential in improving building performance, in terms of providing daylight, reducing unnecessary solar heat gain and also generating electricity onsite. However, low cell efficiency remains an obstacle for their applications in windows. Using light trapping structures in DSSCs shows the potential to improve solar to electrical conversion efficiency. In this work, different pyramid-patterned titanium dioxide (TiO2) geometries are designed to enhance the photon absorption in DSSCs, and characterised using a Monte-Carlo algorithm based 3D ray-tracing simulation. Various studies were carried out under average irradiation, spectrum dependent irradiation and different solar incidental angles, respectively. The simulation results at the average irradiation wavelength (540 nm) were compared to those from a previous study using Scanning Photocurrent Microscopy (SPCM) and a reasonable agreement has been achieved. It was found that the structure based on the pyramid array of side wall angle 54.7° can significantly enhance light absorption by up to ~25% and the maximum achievable photocurrent density (MAPD) by up to ~45% across the spectrum of 380-800 nm, when compared to a planar control counterpart.

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