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.