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Highly Efficient Solar Cells Thanks To Solid Foundation

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KIT Researchers Develop Novel Transport Layer for Highly Efficient Perovskite Solar CellsTransparent, electrically conductive, and selective to one type of charge carriers: these are the properties of hole transport layers for Perovskite solar cells. (Photo: Tobias Abzieher, KIT)

The sun is an inexhaustible and sustainable source of
energy. Hence, photovoltaics is gaining importance in German energy production.
Among promising materials for solar cells - with a high efficiency and low
production costs - are metal-organic Perovskites. Researchers of Karlsruhe
Institute of Technology (KIT) have developed a novel type of highly efficient
nickel oxide hole transport layer that can be deposited on large areas and
reaches record efficiencies in these solar cells.

With efficiencies above 24% in the laboratory, Perovskite
solar cells are among the most efficient thin-film photovoltaics systems.
Compared to silicon solar cells that presently are predominant on the market,
they can be produced much easier and at reduced cost.

When sunlight hits the Perovskite absorber, electrons are
detached from their bound state and subjected to excitation. At the same time,
positively charged holes remain. “To gather energy from the solar cell, these
electrons and holes have to be removed on different sides of the absorber. In
Perovskite solar cells, this is done by selective charge carrier layers, i.e.
membranes that allow either electrons or holes to pass,” says Tobias Abzieher,
doctoral researcher at the Light Technology Institute (LTI) of KIT. “Efficient
Perovskite solar cells do not only require an optimized light-absorbing
Perovskite layer, but also optimized charge carrier-selective layers.”

Together with other scientists of KIT, Abzieher has
developed a new type of highly efficient hole transport layer based on nickel
oxide (NiOx) for Perovskite solar cells. This layer can be produced at low
costs and contrary to conventional organic materials, it is less sensitive to
temperatures of more than 70°C. “To deposit the material on the substrate, we
use a vacuum process technology, electron beam evaporation. By means of
evaporation, metal oxide is deposited on a substrate. Thanks to the small number
of process parameters, we can produce large homogeneous layers of constant high
quality,” Abzieher says.

Record Efficiencies

The completely vacuum-processed Perovskite solar cells reach
efficiencies of up to 16.1% and, hence, they are among the most efficient
Perovskite solar cells produced by this method. Apart from vacuum deposition,
the highly efficient substrate also is ideal for absorber deposition by inkjet
printing, a printing method widely used. With this well-known method,
scientists reached a world record: their inkjet printed absorber layers reached
efficiencies of up to 18.5%. “Presently work focuses on the deposition by
rotary coating. Here, efficiencies are above 24%. However, this technology
cannot be transferred to large areas,” Tobias Abzieher says.

“We concentrate on scalable production methods. Our goal is
to transfer Perovskite photovoltaics from the laboratory to the factories,”
says Dr. Ulrich W. Paetzold, Head of the Advanced Optics and Materials for Next
Generation Photovoltaics Group of KIT's Institute of Microstructure Technology
(IMT) and Light Technology Institute (LTI).

Apart from KIT, the Heidelberg Innovation Lab is involved in
the project. Research was funded by the Federal Ministry of Education and
Research (BMBF), the Helmholtz Association's Initiative and Networking Fund,
and Karlsruhe School of Optics & Photonics (KSOP).

Original Publication:

Tobias Abzieher, Somayeh Moghadamzadeh, Fabian Schackmar,
Helge Eggers, Florian Sutterlüti, Amjad Farooq, Danny Kojda, Klaus Habicht,
Raphael Schmager, Adrian Mertens, Raheleh Azmi, Lukas Klohr, Jonas A.
Schwenzer, Michael Hetterich, Uli Lemmer, Bryce S. Richards, Michael Powalla,
and Ulrich W. Paetzold: Electron-Beam- Evaporated Nickel Oxide Hole Transport
Layers for Perovskite-Based Photovoltaics, Advanced Energy Materials, 9,
1802995, 2019


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