Deschler - Research
Group leader: Dr. Felix Deschler - Emmy Noether Fellow
A recent material focus of our work are hybrid semiconductors, in particular the hybrid perovskites,
which represent an exciting class of sustainable semiconductors with a range of
surprising physical characteristics. We fabricate these materials in-house using
solution-based self-assembly, which creates new opportunities for tailoring electronic states and interfaces for opto-electronic applications.
Employing our expertise in solid state physics and
materials science, and driven by a passion to answer fundamental physical
questions, we have recently made key discoveries on the physical origins of the
exceptional properties of the hybrid perovskites, e.g. their high luminescence
yields. Beyond the hybrid perovskites, we have
considerable interest and made high impact contributions in emerging energy
materials exhibiting strong localization (i.e. organic molecular
semiconductors), local probes of excitation dynamics in nanostructures, and
novel architectures for opto-electronic devices.
Cross-cutting these themes is the development and application of novel tools for characterization of nanoscopic interactions in hybrid materials, in which disorder is inevitable and often governs function. These advanced methods, ranging from near-field approaches in high-resolution optical spectroscopy to facility-based time-resolved scattering measurements, are used to elucidate elementary steps in functional materials across various length, time, and energy scales.
We are currently exploiting the opportunities arising from the
versatile perovskite material platform to address fundamental knowledge gaps
and aim to achieve breakthroughs in material physics in the following areas:
|A. ||Overcoming fundamental challenges associated with charge localization in novel semiconductors to maximize control of luminescent recombination in materials for optoelectronics|
|B.||Synthesizing and characterizing hybrid magnetic semiconductors to answer open questions regarding spin-interactions within functional materials for green spintronics and information storage|
|C.||Understanding fundamentals steps of charge-to-ion conversion in photoactive battery electrode materials and operating electrochemical devices|
Photodoping Enables Efficient Luminescence in Alloyed Perovskites
reported that mixed-halide perovskites show high luminescence yields for carrier
densities far below solar illumination conditions. Supported by microscale
mapping of the optical bandgap, electrically gated transport measurements and
first-principles calculations, we demonstrate that spatially varying
energetic disorder in the electronic states causes local charge accumulation,
creating p- and n-type photo-doped regions, which unearths a strategy for
efficient light emission at low charge-injection densities. Contrary to common believes, disorder in the alloyed perovskites proves beneficial for their optoelectronic properties.
Probing Ultrafast Carrier Thermalization with 2D Electronic Spectroscopy
Nature Communications (2017)
In band-like semiconductors, charge carriers form a thermal energy distribution rapidly after optical excitation. In hybrid perovskites, the cooling of such thermal carrier distributions occurs on timescales of 300 fs via carrier-phonon scattering. However, the initial build-up of thermal distributions proved challenging to resolve with pump–probe techniques due to the requirement of high resolution in time and pump energy. Here, we use two- dimensional electronic spectroscopy with sub-10 fs resolution to directly observe the carrier interactions that lead to a thermal carrier distribution. We find that thermalization occurs dominantly via carrier-carrier scattering under the investigated fluences and report the dependence of carrier scattering rates on excess energy and carrier density.
Photon Recycling in
We have shown that photon recycling, as seen previously in highly
efficient gallium arsenide solar cells, contributes to the exceptional performance of hybrid perovskites. In most
solar cells, the recombination of photogenerated charge carriers (electrons and
holes) wastes all of the energy. In the perovskites, recombination of generated
charges emits a photon that can be reabsorbed and create further charge
the propagation of photogenerated luminescence and charges from a local photoexcitation
spot in thin films of lead tri-iodide perovskites. We observed light emission at
distances of ≥50 micrometers and found that the peak of the internal photon
spectrum red-shifts from 765 to ≥800 nanometers. Thus, energy transport is not
limited by diffusive charge transport but can occur over long distances through
multiple absorption-diffusion-emission events.