The efficiency of a solar cell can decisively be increased by a surface
structuring process. A novel laser based technology to structure
organic solar cells has proved itself as a very fast and efficient
process and is thus very promising for industrial applications.
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| The direct laser beam interference pattering method (DLIP) transfers nanostructures in one step into metals, ceramics or
polymers. |
In recent years the photoelectric efficiency of organic photovoltaics
has made enormous progress. The technology offers the scaling potential
to large and flexible photovoltaic substrates. Further efficiency
improvements are expected from optimizing the intrinsic properties of
the organic material. Micro- and nanostructured surfaces are very
advantageous for organic solar cells since they increase the optical
path length for the incoming light within the active material.
The scientists at the Fraunhofer IWS apply a very fast and efficient
technology with short processing times at increased resolutions, the
so-called direct laser beam interference pattering method (DLIP). The
method transfers nanostructures in one step into metals, ceramics or
polymers. Making an interference structure requires at least two
collimated and coherent laser beams, which superimpose on the substrate
surface. Interference occurs throughout the entire superposition volume
of the beams. A single laser pulse can process a surface area of up to
several square centimeters, which leads to an effective structuring
speed of several square centimeters per second.
In close cooperation with the Institute for Applied Photo Physics
(IAAP) of the Technische Universität Dresden the IWS scientists
investigated the influence of the DLIP structuring procedure on the
efficiency improvement of organic cells on PET foils. It proved that
the efficiency of solar cells on structured substrates could be
decisively improved. The superposition of two laser beams results in a
linear structure. This procedure achieves an efficiency increase of
appr. 10 % compared to the non-structured PET substrate. Three beams
that are not within the same spatial plane form a point structure. The
structuring period is defined by the angle between two laser beams and
their wavelengths. Crossed structures are made in a two-step process.
First a linear structure is imprinted and then the substrate is rotated
by 90° prior to repeating the same structuring step. This
technology turns out to be especially advantageous for organic cells on
PET foils and leads to an efficiency increase of 21 %.
For the industrial implementation of this procedure the IWS engineers
developed a compact laser interference system, which enables an inline
structuring process.
