Dominik Differt
measuring the scattering of light in a rough absorber film.
Photo: Bielefeld
University
(September 1, 2015) Physicists
study how to achieve perfect absorption of light with the help of rough
ultrathin films
Light-absorbing films can be found in many everyday
applications such as solar cells or sensors. They are used to convert light
into electrical current or heat. The films literally trap the light. Although
such absorber films are applied widely, scientists still do not know which
mechanism permits the most efficient absorption of light. A team of physicists
at Bielefeld University, the University of Kaiserslautern, and the University
of Würzburg have now proved that the very efficient scattering of light in
ultrathin rough films traps light until it is absorbed completely. The
researchers are now publishing their findings in the journal Nature Photonics.
This research can help to make thin absorber films even more efficient and
thereby save energy.
The experiments applied ultrashort light pulses. When such
pulses penetrate smooth ultrathin films, they emerge on the other side
practically unchanged and scarcely weakened. In rough films, in contrast,
irregularities prevent the light pulse from spreading through the material.
When there are many irregularities leading to light scattering, the pulse
proceeds along a closed path and remains trapped until the light is absorbed.
Martin Piecuch adjusting
the electron microscope to detect hot electrons.
Photo: University
of Kaiserslautern
The underlying effect of this so-called Anderson
localization was already described more than 60 years ago, and it has been
observed several times since then. What is new is that the mechanism also
functions for thin absorber layers. ‘This opens up new ways to develop highly
efficient absorbers and can therefore contribute to developing improved
thin-film solar cells or sensors,’ says Professor Dr. Walter Pfeiffer from
Bielefeld University. The idea behind the research is to make thin-film
absorbers more efficient so that they can be used in everyday applications. In
future, the researchers aim to study what structure films should have in order
to trap light perfectly and to use this to develop a universal concept of
efficient light absorption via Anderson localization.