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

Abstract

ABSTRACT:The deposition of perylene diimide-based aggregates (PDI) onto wide band gap n-type Sb-doped SnO 2 (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/cm 2 net photocurrent at 1 V vs SCE) compared to both WO 3 -PDI and undoped SnO 2 -PDI when used in a photoelectrochemical setup for HBr splitting. Although ATO, SnO 2 , and WO 3 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 WO 3 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 IrO 2 -modified ATO-PDI photoanodes.

Electronic Properties of Electron-Deficient Zn(II) Porphyrins for HBr Splitting

“…Sci. 2019, 9,2739 3 of 23 was allowed to react at RT overnight. Then, 12.8 mmol of DDQ (2.90 g) in dry CH 2 Cl 2 (100 mL) were added and the mixture was refluxed for 2 h under N 2 .…”

“…After cooling these substrates at room temperature, the SnO 2 paste was blade cast onto them to obtain a wet film, which was fired at 500 • C for 30 min, leading to a mesoporous network composed of SnO 2 . 9 Finally, an overlayer of TiO 2 , serving both as a passivation layer and to improve dye adsorption, was formed by immersion of the SnO 2 films in an aqueous 0.4 M Titanium tetrachloride (TiCl 4 ) solution for 12 h, followed by rinsing with DI water and heating at 450 • C for 30 min. Staining of the resulting photoanodes was carried out by immersion in a 2 µM solution of each porphyrin in a toluene/ethanol 1:1 mixture containing 2 × 10 −5 M chenodeoxycholic acid as an anti-aggregating agent.…”

“…In particular, along with the widespread photoinduced water splitting reaction [3,4], the splitting of hydrohalic acids (HX) in photoelectrosynthetic cell (PEC) set-ups has grown in interest among the scientific community [5][6][7]. Among the possible reactions, HBr splitting is the most promising [8,9], since the oxidation reaction yields Br 2 , a liquid product easy to transport for its further use in fuel cells [10].…”

“…Photoanodes for bromide oxidation include TiO 2 or SnO 2 /TiO 2 core-shell nanostructures functionalized with ruthenium polypyridyl based photosensitizers [11], as well as WO 3 , SnO 2 , and Sb-doped SnO 2 decorated with aggregated dyes belonging to the family of perylene diimides, reaching up to 1 mA/cm 2 photocurrent [9].…”

Gelation enabled charge separation following visible light excitation using self-assembled perylene bisimides

“…A particularly attractive feature of PBIs is that they readily aggregate into structures consisting of p-stacked molecules, which can in principle enable both exciton and long-range charge transport through the structure. [7][8][9][10] Designing functionality onto the PBIs that directs self-assembly offers a route to control the nature of the aggregates formed. This is important as changes in aggregate type, size or in the interlayer distance between the PBI units of the aggregate can have a profound effect on the photophysics and charge transport properties of the materials.…”