The continued advances in energy- and time-
resolved spectroscopy have allowed the
detailed interrogation of photoinitiated
molecular processes in real time, and provided
insight into molecular and chemical processes
in photoelectrochemical and catalytic systems.
The advent of scanned probe microscopy has
enabled, on the other hand, both structural and
functional imaging of various physical
processes with near-atomic precision. These
tools, combined with advances in
nanofabrication techniques, have allowed the
direct visualization of charge transport and
charge trapping in nanoscale systems, and
provided functional snapshots of critical events
in photovoltaic devices.
Continued and vigorous efforts to develop and
extend these experimental tools are essential for
solar energy research. Prominent examples that
need to be developed further include X-ray and
transmission-electron-microscope tomography,
which will allow the determination of three-
dimensional structure of individual
nanostructures with atomic precision.
Nanoscale components play important roles in
many solar energy conversion systems,
including organic and hybrid photovoltaic cells,
photoelectrochemical cells, and photocatalytic fuel generation; the new capability afforded by
atomic resolution tomography will facilitate the design and characterization of nanostructures
with improved functionalities.
Another important experimental tool that is currently lacking is scanned probe techniques with
chemical specificity. In many photoelectrochemical and catalytic systems, the chemical
processes that occur at electrode-solution interface play a quintessential role. Scanned “chemical-
probe” microscopy should allow the discrimination of distinct chemical species in complex
environments and hence, the monitoring of interfacial chemical reactions with nanoscale
resolution. The knowledge gained in these studies should then provide detailed new insight into
characterizing and optimizing solar fuel systems, an important ingredient of a viable solar energy
future.
In addition to developing experimental tools with new capabilities, significant efforts should also
be directed toward integrating functionalities of distinct experimental tools to enable
simultaneous structural and functional imaging of solar energy conversion systems with requisite
time resolution. This integration effort is all the more critical because most current experimental
tools are limited to the characterization of individual components and processes and fail to
provide system-wide insight into the structure and function of solar energy conversion systems.
Figure 51 Emerging experimental tools:
(a) scanned gate (left) and electrostatic force
(right) microscopy images of individual
nanostructures that allow the combined
structural and functional characterization of
individual defects; (b) schematic diagram of
X-ray nanoprobe (ANL) that will allow the
structural characterization of nanoscale
structures.