Energetic alignment of buried junctions and tailored interfaces in photoelectrochemical multi-junction devices

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This project seeks to elucidate the electronic structure and energetic band alignment at the hetero-interfaces of photoelectrochemical multi-junction devices. Comprehension of the band energy diagrams of photoelectrochemical devices in the vicinity of the electrolyte with respect to their relative energetic position as well as the formation of electronic surface states will help to understand efficiency-limiting factors of the overall device. The coupling of absorbers to chemical and electronic passivation layers as well as co-catalysts will be systematically studied, primarily by electrochemical methods coupled in-vacuo to photoelectron spectroscopy. Density functional theory will allow an in-depth interpretation of experimental data, finally providing an atomistic view on the origin of energetic alignments. As the elementary processes of light absorption, charge-separation and -transfer, as well as multi-electron catalysis are highly interrelated, we will focus on two established water splitting multi-junction devices that have already demonstrated high efficiencies, but still have not reached the physical limits: silicon-based multi-junction as well as III-V compound semiconductor-based tandem cells. The hereby identified routes to modify the electronic coupling of the hetero-interfaces will, in close cooperation with the other partners, also be studied and evaluated under operating conditions. For the long-term perspective of the Research Consortium, this project will provide generalised research approaches that can be transferred to other high-efficiency multi-junction systems.