Scanning photocurrent microscopy of 3D printed light trapping structures in dye-sensitized solar cells

Abstract

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%.

Design and optical characterisation of an efficient light trapping structure for dye-sensitized solar cell integrated windows

“…Simulation results at this wavelength show 16% more total light absorbed, or an enhancement in absorption by ~22%. Experimental results (Knott et al 2018) show enhancement in photocurrent generation up to maximum of ~25% although mean enhancement is lower at ~10%. Both results show reasonable agreement, with experimental work showing lower photocurrent enhancement than the absorption enhancement in the simulation as expected, indicating the model is effective.…”

“…3D ray-tracing models are developed for our light trapping designs which have been incorporated into a DSSC device (Knott et al 2018). The device consists of a glass substrate with a transparent conducting FTO coating, TiO 2 active layer, electrolyte and finally another FTO coated conducting glass back contact.…”

“…The ray-tracing simulation results begin with a model of our light trapping designs which were used for the fabrication of patterned electrodes (Knott et al 2018). These structures have a side wall angle of 54.7°, height 5 μm and base diameter 8 μm.…”

“…In this study, we adopt a 3D ray-tracing technique based on Monte-Carlo algorithm to investigate the light trapping effectiveness of the designed DSSCs based on periodic pyramid-patterned TiO 2 films. The DSSC performance at a single wavelength (540 nm) is simulated and compared to the SPCM results obtained in the previous work (Knott et al 2018). The DSSC performance at different incident light angles, over AM1.5 solar spectrum and with different pyramid geometries are also evaluated.…”

“…Moreover, a wavelength-selectivity of light trapping was observed when changing the grid spacings, which may be attributed to the mismatch between the spectrum of light scattered by the patterns and the dye absorption spectrum. Recently, Knott et al (2018) utilized a submicron 3D-pinting technique known as Two-Photon Polymerization (TPP) to develop light trapping structures for DSSCs. In the study, periodic pyramid-patterned TiO 2 microstructures were prepared and tested by the Scanning Photocurrent Microscopy (SPCM) experiments and showed significant enhancement effect of up to ~25% on photocurrent in the cell when compared to a non-patterned planar structure.…”