Nanophotonic approaches to colourful solar cells and modules

The focus of this work was first to compile a literature review of the most relevant nanophotonic approaches proposed to realize structural colours for decorative and building-integrated solar cells and modules. Then, based on the gathered information, an alternative fabrication technique was proposed and experimentally investigated. From the literature review it was observed that the fabrication of colourful solar cells had been successfully achieved by integrating light filtering structures showing reflective structural colours (as opposed to light absorbing colours, e.g. dyes and pigments or metals), with different photovoltaic technologies. In general, the exploited light filtering mechanisms can be divided in multilayer interference, thin-film interference, diffraction gratins, plasmonic resonance and photonic bandgap in photonic crystals. The best results in terms of performance of the fabricated coloured devices had been obtained when the colouring structures had been integrated with standard, industrial crystalline silicon solar cells. On the other hand, advantages in terms of device thickness (amount of needed material) and colour purity had been obtained when the coloring structures had been used with a customized fabricated device (thin-film amorphous silicon solar cells, dye sensitized solar cells and perovskite solar cells). In the experimental part, a proof-of-concept was presented for the fabrication of a colour filter by inkjet-printing three dimensional photonic crystals on glass. A colour filter fabricated in this way could be used with all photovoltaic technologies, since it consist of a separate semi-transparent layer that can placed over any kind of solar cell. The structure was realized by inkjet printing, which allows flexible control over pattern design and accurate material deposition, allowing for the possibility of printing multi- and single-coloured patterns on a photovoltaic device. According to the preliminary results, further research would be needed to intensity of the coloured reflection and weaken the broad-band light scattering by the inkjet-printed photonic crystals.