Charge carriers in
polymeric carbon nitrides always take paths perpendicular to the sheets,
as Merschjann’s
group has now shown. Light creates an electron-hole pair. The opposite
happens when an
electron and hole meet under certain conditions (forming a singlet exciton)
and emit light
(fluorescence). A graphene lattice is shown in the background.
Image: C.
Merschjann
(November 12, 2015) Joint project details charge transport
in polymeric carbon nitride for first time
Polymeric carbon nitride is an organic material with
interesting optoelectronic properties. As an inexpensive photocatalyst, it can
be used to facilitate water splitting using sunlight. Joint research by
Helmholtz-Zentrum Berlin, the University of Rostock, Freie Universität Berlin
as well as other partners has now investigated for the first time how light
creates charge carriers in this class of materials and established details
about charge mobility and lifetimes. They discovered surprising characteristics
in their investigations that provide prospects for new applications, in
conjunction with graphene for example.
Polymeric carbon nitrides are organic compounds synthesised
to form a yellow powder of a myriad of nanocrystals. The crystalline structure
resembles that of graphite because the carbon nitride groups are chemically
bound only in layers, while just weak Van der Waals forces provide cohesion
between these layers. It was already known that light is able to create an
electron-hole pair in this class of materials. So there have already been
numerous attempts to employ polymeric carbon nitrides as cost-effective
photocatalysts for solar-powered water splitting. However, the efficiency
levels so far have remained comparatively low.