Photo-electrochemical and photocatalytic technologies are promising solutions for solar fuel production and involve a number of physical and chemical phenomena. We provide an overview of numerical and analytical tools to describe such phenomena occurring at disparate time and space scales within devices such as photoelectrochemical cells and photo-chemical reactors. On one hand, chemical phenomena include photo-induced electron transfer, charge separation, recombination, equilibrium reactions between species in solutions and adsorption reactions. On the other hand, examples of physical phenomena are the transport of chemical species or self-assembling of molecular structures. In this respect, we critically review macroscale continuum models for transport phenomena combined with kinetic descriptions including their possible coupling with models at even lower scales. We specifically focus on atomistic and coarse-grained models able to represent the local environment of the reactive interfaces such as photoelectrodes or supra-molecular assemblies. The critical role of the latter structures on photochemical conversion is highlighted: Therefore, morphological structure of self-assemblies, such as micelles and monolayers, in solution and at the solid–liquid or gas–liquid interfaces are also discussed. Finally, important scientific gaps are identified and possible perspectives for future research outlooked.