Better Solar Cells
Organic solar cells based on conjugated polymers are promising
candidates for efficient low-cost photovoltaics, and have recently
reached power conversion efficiencies exceeding 6%. This is a
formidable achievement, considering that the light-generated positive
and negative charges are expected to be hardly separable, as they
attract each other much more strongly than in inorganic materials. In
our paper, we show why the separation of the charge pairs is so
efficient. Our considerations are based on a computer programme, a so-
called Monte Carlo simulation, by which the complex movement of charge
pairs in polymer-fullerene solar cells can be approximated very well.
We show that if the one constituent of a charge pair sits on an
polymer chain segment, it is attracted by the other charge the less
the longer the polymer chain is. This leads to the very efficient
separation of the charge pairs. Indeed, our simulations show a ten-
fold improvement of the resulting photocurrent when increasing the
length of the polymer chain segment from 1 to 10 nanometers, the
latter being a typical value for a conjugated polymer. Thus, our
findings explain why state-of-the-art polymer based organic solar
cells show such a good conversion of light to current.
***
LW11716
Liquid Jets from Nanorumbles Could Form Next Generation Inhalation Therapy
or Ink-Jet Printing Devices
Nanometer amplitude sound waves that travel on the surface in a manner
similar to earthquakes could very soon be exploited to effectively deliver
drug-laden aerosols and powders to our lungs or for ink-jet printing.
These nanometer 'surface acoustic waves', as they are known, are focussed
underneath a millimeter sized liquid drop. The very efficient transfer of
sound energy into the liquid then results in the generation of a
cylinder-like liquid jet that protrudes from the drop and persists over
centimeters in length. The jet then breaks up into micrometer sized
aerosol droplets as it stretches. As the liquid can act as a carrier for
drugs or even consist of ink or fuels, these surface acoustic waves could
well be on the way to comprise the next-generation inhalation therapy,
ink-jet printing or fuel injection devices.
***
LX11325E
Water-walking machine
We report the generation of directed self-propelled motion of a droplet
of aniline oil with a velocity on the order of centimeters per second on
an aqueous phase. The self-propelled motion persists for hours. The
droplet is preferred to control. It is promise that the self-propelled
motion will inspire the design of water-walking machine and transporter.
It is found that, depending on the initial conditions, the droplet shows
either circular or beeline motion in a circular Petri dish. The motion
of a droplet depends on volume of the droplet and concentration of
solution. The velocity decreases when volume of the droplet and
concentration of solution increase. Such unique motion is discussed in
terms of Marangoni-driven spreading under chemical nonequilibrium.
***
LA12348
A gravitational wave detector probes fluctuation theories of
nonequilibrium systems
Dissipative systems, like motors or living cells, need a power input to
sustain their functions. When the system is small, this power heavily
fluctuates around its mean value, due to the noisy imprint of the
underlying atomistic nature. However a system must not be necessarily as
small as a pollen particle to be dominated by microscopic fluctuations:
in this paper we use a ton-size resonant gravitational wave detector as
a test bench for statistical mechanics theories. First, we analyze the
active cooling scheme used to keep the Auriga detector at an effective
temperature of 20 milli-Kelvin (20 thousandths of a degree above
absolute zero), showing that it sustains an energy flow through the
system. Then, we study the fluctuations of the power exchanged with the
surroundings, reporting data obtained from the output of the detector
since the beginning of its operation in 2005. The availability of such a
large amount of experimental data make possible the analysis of rare
fluctuations, and gives a clear evidence for a model recently proposed
to describe power injection phenomena.
