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