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Department Optics for Solar Energy

The Department

At the Department Optics for Solar Energy (SE-AOPT) we work on experimental and numerical optics in and for photovoltaic devices. From an optical point of few the Sun is a challenging energy source: solar energy devices have to be optimized for a broad spectral range and for a light source changing the illumination direction during the course of the day and the year with varying shares of direct and diffuse irradiance.

This requires advanced optical concepts ranging from “conventional” ray optics to nanophotonic concepts and spectral conversion. Our reseach brings together experimental expertise—mainly nanoimprint lithography—and optical simulations. Our current research topics include light management in perovskite solar cells and perovskite/silicon tandem solar cells, antireflective microstructures, energy yield calculations, and photon upconversion

Currently, the department is – amongst others – member of the Helmholtz Innovation Lab HySPRINT, participates in the Helmholtz Einstein Berlin Research School in Data Science (HEIBRiDS) and is a leading member of the Berlin Joint Lab for Optical Simulations for Energy Research (BerOSE) between HZB, the Zuse Institute Berlin (ZIB) and the Free University Berlin

Research topics

Light management in perovskite/silicon tandem solar cells

Nanotextured perovskite/silicon tandem solar cell

A textured perovskite/silicon solar cell. Picture: J. Sutter / HZB.

Perovskite/silicon tandem solar cells are a promising concept to surpass the efficiency limit of silicon solar cells, the most widespread solar cell technology. Tandem solar cells allow to harvest the broad solar spectrum more effectively, because the the energy of short-wavelength photons can be utilized more efficiently.

Light management aims to minimize optical reflection and transmission losses in solar cell devices. In order to achieve this, we build solar cells with one- to three-dimensional photonic nano- and/or micro-structures, which are specifically tailored for the respective device structure and its wavelength regime. In addition, the influence of the optical structures on the electronic material properties as well as the interfaces are always taken into account.

In collaboration with Steve Albrecht's Department Perovskite Tandem Solar Cells and the silicon solar cell group at PVcomB led by Bernd Stannowski, we managed to build a perovskite/silicon tandem solar cell with 29.8% power conversion efficiency. This was the world record between November 2021 and July 2022.

Key publications

Optical optimization of bifacial solar power plants

Solar fence with bifacial solar modules

Bifacial solar modules, which are installed as a solar fence. Picture: K. Jäger / HZB.

Photovoltaic (PV) systems consisting of bifacial solar modules can generate a significantly higher annual energy yield than systems using conventional monofacial PV modules, because bifacial solar modules not only utilize light impinging onto their front, but also illumination onto their rear side.

Bifacial solar cells allow to increase the output power of PV systems at low additional costs and are hence on the march to dominate the PV market soon. In our department we work on optical optimization of bifacial solar panels and hence on decreasing the levelized cost of electricity (LCOE) further. To achieve this we combine advanced optical simulation models with global solar irradiance data using modern computational optimization algorithms.

Key publications

Photon up-conversion and optical sensing

A mode around a photonic crystal with quantum dots

Full-3D volume renderings of an electric field mode around a photonic crystal. A closer view indicates a random distribution of quantum dots (bright small spheres), emitting white light with an intensity proportional to the field energy density at their specific positions. Picture: C. Barth / HZB [Communications Physics 1, 58 (2018)]

Photon up-conversion enables harnessing parts of the solar spectrum in the near infrared wavelength regime, which cannot be absorbed by silicon. Such spectral conversion processes, however, require a large excitation power densities that can hardly be achieved at 1 Sun illumination conditions.

Photonic nanostructures provide extremely strong near-field enhancement rendering photon up-conversion at low intensity conditions possible. In the Department optics for Solar Energy we aim to increase the light yield of emitters by engineering the local density of photonic states close to the surface or inside the photonic nanostructure. This effect can be utilized for numerous applications based on photonic up- and down-conversion, such as solar energy and optical sensing.

Key publications