Proceedings of the European Summer School of Photovoltaics 4 – 7 ...

Fig. 2. CNT layer resistivity changes during dynamic bending [4]
electrode design. Additionally, the development of simulation
models for certain types of solar cells with carbon nanotube
contact would be implemented.
Some preliminary results shown in Fig. 1 and 2 have already
been achieved. Obtained layers showed sufficient optical transparency
(Fig. 1) and insensitivity of its electrical resistivity for dynamic
bending (Fig. 2).
– As a second stage of research work, complete thick and thin
film photovoltaic structures with transparent carbon nanotube
based electrode, will be manufactured. Scheduled domain of
study includes production of traditional silicon PV cells, as well
as inorganic thin film structures, CIS solar cells. Constructed
solar cells would enable a comprehensive examination of new
carbon nanotube contacts, in elastic and rigid structures, as well
as comparison to traditional electrodes. The structure of manufactured
devices will be examined by using advanced measurement
techniques. Optoelectronic parameters will be measured
with calibrated testing equipment in standard test conditions.
– On the basis of obtained results, indispensable corrections of
composition and/or deposition technique will be applied, as
well as theoretical models describing phenomena in test solar
cells will be verified.
As a result of the project a description of production technology
for using CNT in each of examined solar cell structures will
be created.
Polonium: New solutions for solar cells down
converters
Polonium is an international Polish-French program granted by
the Polish Ministry of Science and Higher Education, French Ministry
of Foreign Affairs and French Ministry of Higher Education
and Research. However, the financial support is only given for
the scientists cooperation and personal exchange, but not for
research.
This project is currently realized by the team of DSOD Lodz
in the cooperation with the Lyon Institute of Nanotechnology of
INSA Lyon in France. It has been granted for years 2012 and
2013.
The aim of the project entitled: “New solutions for solar cells
down converters” is to improve solar cell performance by the
use of novel solution for light capture. We proposed the application
of a film, composed of ZnO nanoparticles (NPs), as a down
converting layer, for enhancing external quantum efficiency and
conversion efficiency of a photovoltaic device. Preliminary research
showed that ZnO nanoaggregates have a great potential of
application as down converting layers. Investigations performed
on a zinc oxide nanoparticle layer, proved that it generates several
low-energy photons out of every high-energy incident photon.
Optical down conversion, by ZnO nanoparticles should enhance
solar cell efficiency by converting ultraviolet sunlight into visible
light, which is more effectively used by the device (solar cell quantum
efficiency is lower in the UV region than in visible zone, due to
front surface recombination of hot photocarriers). Basic research
of ZnO nanoparticle converters on silicon test structures are currently
being realized [5].
Fig. 3a presents the simplified band diagram of a down converting
material placed above a solar cell. In this system, absorbed
photons are reemitted as two lower energy via a midgap splitting
level in the down-conversion process [6]. The idea of using this in
single junction solar cell is schematically presented in Fig. 3b.
Further research aiming the increase of the solar cell efficiency
will be concentrated on the development of novel photovoltaic
devices using ZnO nanoparticle down converters in tandem
solar cell. We will investigate new type of tandem devices
including zinc oxide nanoparticles. ZnO NPs layer is supposed
to be located under the top junction in order to efficiently capture
and convert solar light, which is than partially forwarded to
the bottom junction and partially reflected back and thus can be
used by the top cell.
Another idea concerning the use of ZnO nanoparticles as
down converters is their introduction into metal-semiconductor
solar cells. Forecasted studies include theoretical investigations
(computer simulations) and practical realization of the final device
ZnO NPs-metal-semiconductor solar cells.
Projects proposals submitted for financing
The DSOD’s team of photovoltaics applied for two another
projects financing in programs funded by the National Science
Centre. One of them is national Preludium program, which
is dedicated for pre-doctoral grants. Second is an international
project for non co-financed international grants, called Harmonia.
It is going to be realized in cooperation with the University
of INSA Lyon in France. Decisions on financing in both National
Science Centre programs are planned to be announced in the
end of July 2012.
Fig. 3. Down-conversion system: a) band diagram, b) schematic of a down-converting layer consisting of nanoparticles, placed on top of
a pre-existing solar cell [6]
Elektronika 6/2012 135