p-TYPE enabled us to develop two rapid and controlled routes to new semiconductor materials and morphologies to obtain libraries of compounds from which those with desired properties can be selected. We conducted a suite of experiments with these materials, including new screening protocols, to determine the structure property relationships which affect electron transfer and hole transport in p-type semiconductors. To make these experiments consistent, it was important that the synthesis routes enabled us to control, reliably and reproducibly, the different electronic and morphological properties of the materials in the library. We used a custom-made co-precipitation reactor where precursor salts were premixed before entering the reactor, where they were hydrolysed to form mixed metal hydroxides, which were collected and formulated into printable inks for applying in solar cells. For some classes of material and for depositing thin, uniform films on electrodes, this route was not always appropriate, so we built an automated ultrasonic spray system. Our third alternative was to automate successive ionic layer adsorption and reaction (SILAR), which can be used to grow or coat thin films of semiconductors This was mostly successful for light absorbing components, such as metal sulfides (Sustainable Energy and Fuels, 2019).
The ability to print metal oxide materials onto flexible substrates, particularly carbon cloth, stimulated the idea of developing wearable solar cells. This successful concept has captured the imagination of the public and Royal Air Force stakeholders. It inspired us to miniaturise our outdoor testing facility so that it could be worn (with the solar cells) by a person to evaluate the power that could be harvested to power a portable electronic device (e.g. for communication). Very few (if any) groups have been able to provide live data in this way that provides information for decision makes regarding how the technology could be developed and implemented. This has been showcased to the public at air shows including The Royal International Air Tattoo in 2022 and 2023 and the Miramar air show (San Diego) in 2022.
We have shown how combining molecules with metal oxide clusters or nanoparticles can be used to store charge so that it can be used to generate power in a solar cell or fuels from water, carbon dioxide and sunlight. Advanced spectroscopy allowed us to prove how careful control over the composition, structure and environment enabled us to accelerate the separation of charge and slow down charge recombination to improve the performance of devices. We have also been able to increase the performance of light-active electrodes that generate hydrogen or synthesis gas. This approach enables us to store the energy from sunlight over day-night or seasonal cycles and potentially could provide the feedstocks for fossil-free chemicals in the future.
We have presented results at several major national and international conferences including the American Chemical Society, Materials Research Society, Royal Society of Chemistry and Royal Society Meetings. We have also carried out public engagement activities to showcase our research at the Royal Society, Science Museum London and the Great North Museum (Hancock) Newcastle. We also worked on technology transfer and hosted an intern from an international company, who we trained to make flexible solar cells.
