Abstract
Abstract Photoelectrochemical water splitting is a promising solution for harnessing solar radiation for hydrogen production. Copper oxide semiconductors, particularly materials based on cuprous oxide, have attracted attention due to their abundant elemental availability and scalable synthesis methods. To improve the generated photocurrent of the photoelectrode system, photon upconversion materials can be implemented into water-splitting devices. Here, we demonstrate the potential application of triplet-triplet annihilation-based upconversion in solar-assisted water splitting and highlight the significance of photonic designs to improve the light-harnessing properties of photoactive materials. The triplet-triplet annihilation mechanism is particularly suitable due to its efficient conversion at low photon intensity, namely under 1-sun illumination. Our results show that Cu2O coupled with an upconverter outperforms bare Cu2O by 56% in terms of produced photocurrent density. We construct a hybrid water-splitting device with an extended absorption range by utilizing a semi-transparent 600 nm Cu2O film with a 5 nm Au underlayer.