Perylene Diimide Aggregates on Sb-Doped SnO2: Charge Transfer Dynamics Relevant to Solar Fuel Generation

The deposition of perylene diimide-based aggregates (PDI) onto wide band gap n-type Sb-doped SnO2 (ATO) was investigated with the aim of finding efficient and versatile dye-sensitized platforms for photoelectrochemical solar fuel generation. These ATO-PDI photoanodes displayed hydrolytic stability in a wide range of pH (from 1 to 13) and revealed superior performances (up to 1 mA/cm2 net photocurrent at 1 V vs SCE) compared to both WO3-PDI and undoped SnO2-PDI when used in a photoelectrochemical setup for HBr splitting. Although ATO, SnO2, and WO3 are endowed with similar conduction band edge energetics, in ATO the presence of a significant density of intrabandgap states, whose occupancy varies with the applied potential, plays a substantial role in tuning the efficiency of photoinduced charge separation and collection. Furthermore, the investigation of the charge injection kinetics confirmed that, even in the absence of applied bias, ATO and WO3 are the best substrates for the oxidative quenching of poorly reducing PDI excited states, with at least a fraction of them injecting within <200 fs. The charge-separated states recombination occurs on longer time scales, allowing for their exploitation to drive demanding chemical reactions, as confirmed in photoelectrochemical water oxidation using IrO2-modified ATO-PDI photoanodes.