Tailoring Photophysical Properties of Diketopyrrolopyrrole Small Molecules with Electron-Withdrawing Moieties for Efficient Solar Steam Generation

Abstract

The development of photothermal materials (PTMs) for solar steam generation (SSG) has gained tremendous attention in response to the global clean water scarcity issue. However, the investigation in employing organic small-molecule PTMs for SSG applications is rarely found due to their narrow optical absorption range to harvest solar energy and insufficient photostability for long-term use. Herein, we employ a diketopyrrolopyrrole (DPP) core unit together with electron-withdrawing (EW) endcaps and siloxane side chains to introduce stronger intramolecular charge transfer (ICT) characteristics as well as the hydrophobic character. The enhanced ICT characteristics of DPP derivatives render a broad optical absorption range, less emission, and a high nonradiative decay rate for efficient solar energy harvesting and photothermal effects. Meanwhile, the hydrophobic nature of these DPP derivatives allows the facile fabrication of novel Janus photothermal membranes for effective water vaporization and solar-to-vapor conversion efficiency. By embedding DPP derivatives to the SSG device, we showed that the solar-to-vapor efficiency can reach up to 71.8% under relatively low visible light power (∼700 W m–2), which is, on average, 2.66 times higher than that of bulk water of similar dimension. Moreover, this report demonstrates the great potential of conjugated small molecules for photothermal applications, owing to their versatility and flexibility in structural engineering and its diminishing radiative decay properties. This may inspire more innovation and advancement in SSG applications.

Towards highly salt-rejecting solar interfacial evaporation: Photothermal materials selection, structural designs, and energy management

“…Until now, the photothermal conversion materials of solar absorbers which have been reported could be divided into four kinds: carbon-based materials [16,23], semiconductors [17,24], and metal-based plasmonic materials [18,25], and conjugated polymers [19,26]. Also, the other photothermal conversion materials, such as aggregation-induced emission (AIE) photothermal molecules [27], conjugated small molecules [28], and metal-organic framework derived photothermal conversion materials [29] have been applied in the solar-driven evaporation field.…”

A brief review on device operations and working mechanisms of organic transistor photomemories

“…67,68 Not only that, the changes of HOMO and LUMO levels could affect the photophysical properties, i.e. , optical band gap, 37,69 and benefitting the device operations with specific photon energy for less light interference.…”

“…Besides, through rationale design and careful selection of the donor and acceptor groups, the energy levels of the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of the resulting molecules/polymers can be finely tuned to match the energy alignment to favor efficient charge transfer. 67,68 Not only that, the changes of HOMO and LUMO levels could affect the photophysical properties, i.e., optical band gap, 37,69 and benefitting the device operations with specific photon energy for less light interference.…”

Engineering Materials to Enhance Light-to-Heat Conversion for Efficient Solar Water Purification

“…Several strategies have been proposed to improve the efficiency of SSG by engineering photothermal materials to have strong light absorption over a wide-frequency band (0.2–3 μm) and high photothermal conversion efficiency, as well as designing a substrate to have good thermal insulation to avoid excessive heat loss and capability to supply water to hot regions. They include chemical regulation ,,− and structural engineering ,− of the photothermal materials as well as solar evaporator design. ,− Chemical regulation of photothermal materials is carried out by introducing different elements or functional groups into the primary photothermal material or compositing two or more photothermal materials. Structural engineering includes assembling photothermal materials to specific architecture for the efficient use of the materials in the solar steam generation system.…”