Sustainable Energy Materials
Photonic Materials
The Photonic Materials group is fascinated by the behavior of light at the nanoscale. We develop novel materials for solar energy conversion and energy-efficient computation and optimize their functionality by controlling the flow of light in them. We develop cathodoluminescence spectroscopy as a microscopy technique to study nanoscale and ultrafast classical and quantum optical materials excitations.
Research focus
The Photonic Materials group studies the flow of light in nanostructured optical metamaterials with specially tailored optical properties. We design and fabricate novel photovoltaic architectures with enhanced power conversion efficiency based on semiconductor and dielectric metasurfaces. These are carefully shaped nanostructures that strongly interact with light.
We also design optical metasurfaces that perform analog optical computing tasks. To gain deeper insight in the nanoscale optical phenomena that are fundamental to our research we have developed angle- and time-resolved cathodoluminescence microscopy.
Cathodoluminescence microscopy uses a focused electron beam to make materials emit light, enabling scientists to characterize materials, structures, and imperfections inside materials at extremely small scales normally invisible to ordinary, optical microscopes.
We study fundamental aspects of the interaction of light with photovoltaic materials, aiming to create solar cells with enhanced efficiency. We design and fabricate nanopatterned layers that are integrated in the solar cell as front or back contact, or as spectrum splitting layer. We also investigate microstructured surface coatings to enhance passive radiative cooling of solar cells. We use cathodoluminescence microscopy to study the characteristics of perovskite solar cells and explore the use of laser annealing to control their crystallization.
We hold the world-record efficiency for a silicon-based solar cell (36,1%), using a triple-juction III-V/Si geometry made by Fraunhofer ISE, with our group designing and fabricating the nanopatterend backreflector. Our initial initiatives in light management in photovoltaic materials were rewarded with the ENI Renewable and Non-Conventional Energy Prize and the NNV Physica Prize.
Our group has developed special cathodoluminescence spectroscopy (CL) instruments that enable the study of nanostructures with deep-subwavelength optical resolution. We use high-energy electrons in a scanning electron microscope (SEM) to excite metal, dielectric and semiconductor nanostructures and study their optical density of states as well as their electronic excited states at the nanoscale. Angle-resolved CL enables momentum spectroscopy at nanoscale spatial resolution, and is complemented with polarimetry and measurements of photon statistics.
Using ultrafast electron beam blanking (>30 ps) as well as femtosecond photo-emission (>1 ps) we create electron pulses that enable time-resolved microscopy at the nanoscale. Ultrafast laser-electron interactions enable shaping of quantum-mechanical electron wavepackets, enabling ultrafast near-field microscopy and correlative experiments in the SEM. We also explore the use of the SEM-CL technique for 3D tomography of materials, including semiconductor integrated circuits. Our CL work was awarded the EPS Science of Light Prize and the MRS Materials Innovation and Characterization Award.
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