The FreeHydroCells project aims to create a new photoelectrochemical system capable of clean, efficient solar-to-chemical energy conversion, with hydrogen gas storing the chemical energy. The system would mimic the solar-energy absorption potential of a leaf by arraying cascades of nanometre thick semiconducting materials as buried pn-junctions that, when submerged in water and exposed to sunlight, are capable of freestanding photoelectrochemical water splitting. A number of technological challenges restrict the cost-effective efficiency of clean, green, solar-to-chemical hydrogen, state-of-the-art systems, making it commercially unattractive, and severely limiting hydrogen’s role in decarbonisation. However, the FreeHydroCells project proposes to leverage a number of advancements in thin film materials, devices, and processes to make similar breakthroughs in photoelectrochemical band-engineering for interconnected bands, defect minimisation, thin film thickness uniformity continuity to minimise drift-dominated transit times, carrier doping for high conductivity, carrier type selectivity and, importantly, preventing significant recombination of light-generated carriers by ensuring drift transport under multiple in-built electric fields. These breakthroughs would transform the transfer efficiency of solar-to-chemical energy via the carefully aligned redox potential and propel the photoelectrochemical water splitting reactions to morph solar energy into hydrogen bonds. The new materials system could be cost-effectively realised through modified delivery techniques of atomic layer deposition and chemical vapour deposition in manufacturing-compatible, large-area capable, equipment that is now common in commercial chip and solar cell processing technologies. FreeHydroCells’ multidisciplinary expertise is key to making this substantial science-to-technology leap: to verify a paradigm proof-of-concept for a self-driven system suitable for up-scaling and commercialisation.