CRC 1073 Atomic scale control of energy conversion
Seminar Series Summer Semester 2025
Please find the programme here
The CRC 1073 in the 3rd Funding Period (01.07.2021 - 30.06.2025)
The overarching goal of the CRC 1073 is to understand and control the elementary steps of energy conversion in materials with tunable excitations and interactions. Our studies focus on new materials systems and conversion routes that are highly promising for future applications in energy conversion and storage but are at an early stage of scientific discovery. Thus, the CRC is a knowledge-driven research initiative in the area of the physical and chemical sciences that contributes to the microscopic understanding of excitations, thermalization and conversion steps down to the atomic scale.
Highlight Publications
The publications presented here prominently represent the overarching goal of the CRC 1073 which is to understand and control the elementary steps of energy conversion in materials with tunable excitations and interactions:
Despite significant advancements in materials design for renewable energy devices, the fundamental understanding of the underlying processes in many materials remains limited, particularly in complex, inhomogeneous systems and interfaces. In such cases, in situ studies with high spatial and energy resolution are essential for uncovering new insights into excitation, dissipation, and conversion processes. Recent progress in in situ atomic scale methods has greatly enhanced the understanding of energy materials. Here, key advances are reviewed, including in situ, environmental and ultra-fast transmission electron microscopy, scanning probe techniques, single-photon-resolved infrared spectroscopy, velocity-resolved molecular kinetics, and in situ grazing-incidence X-ray spectroscopy. These techniques enable the study of energy conversion with spatial resolution from nanometers down to individual atoms, energy resolution down to meV, and single-quantum detection. Especially they enable access to processes that involve multiple degrees of freedom, strong coupling, or spatial inhomogeneities. They have driven a qualitative leap in the fundamental understanding of energy conversion processes, opening new avenues for improving existing materials and designing novel clean and efficient energy materials in photovoltaics, friction, and surface chemistry and (photo-)electrochemistry.
Ultrafast nano-imaging of dark excitons,
Nat. Photon. 19, 187–194 (2025).
Understanding the impact of spatial heterogeneity on the behaviour of two-dimensional materials represents one of the grand challenges in applying these materials in optoelectronics and quantum information science. For transition metal dichalcogenide heterostructures in particular, direct access to heterogeneities in the dark-exciton landscape with nanometre spatial and ultrafast time resolution is highly desired but remains largely elusive. Here we report how ultrafast dark-field momentum microscopy can spatio-temporally resolve dark-exciton formation dynamics in a twisted WSe2/MoS2 heterostructure with a time resolution of 55 fs and a spatial resolution of 480 nm. This enables us to directly map spatial heterogeneity in the electronic and excitonic structure, and to correlate this with the dark-exciton formation and relaxation dynamics. The advantage of the simultaneous ultrafast nanoscale dark-field momentum microscopy and spectroscopy reported here is that it enables spatio-temporal imaging of the photoemission spectral function that carries energy- and momentum-resolved information on the single-particle band structure, many-body interactions and correlation phenomena.
Scaling Behavior in the Spectral and Power Density Dependent Photovoltaic Response of Hot Polaronic Heterojunctions,
Adv. Energy Mater. 2024, 14, 2401189.
Strongly correlated manganites can be considered as model systems for the study of photovoltaic harvesting of hot polarons that can be excited from the electronically ordered ground state. In order to gain basic understanding of hot polaron harvesting, the deviations of the photovoltaic response of a heterojunction with polaronic absorber from a conventional semiconductor are analyzed. Specifically, the spectral and photon power density dependence of the open circuit voltage Uoc and the short circuit current density Jsc in heterojunctions consisting of orbital ordered Pr1-xCaxMnO3 (x = 0.1, PCMO) thin films epitaxially grown on single crystalline (100) SrTiO3 (STO) and Nb-doped (100) SrTiO3 (STNO) substrates are investigated. The observed behavior is fundamentally different from conventional solar cells, in which Uoc is limited by fast carrier relaxation to the band edges. Whereas the spectral and photon power dependence of Uoc of conventional semiconductor junctions is well described by the Shockley-Queisser (SQ) theory, the hot polaron junctions surprisingly show a scaling law behavior of Uoc. Such scaling laws otherwise apply to equilibrium order parameters in second-order phase transitions. It is concluded that its physical origin is the unique dependence of the quasi-Fermi level splitting on temperature, photon energy, and power density in a hot polaron system.
Light-induced hexatic state in a layered quantum material,
Nat. Mater. 22, 1345–1351 (2023).
The tunability of materials properties by light promises a wealth of future applications in energy conversion and information technology. Strongly correlated materials such as transition metal dichalcogenides offer optical control of electronic phases, charge ordering and interlayer correlations by photodoping. Here, we find the emergence of a transient hexatic state during the laser-induced transformation between two charge-density wave phases in a thin-film transition metal dichalcogenide, 1T-type tantalum disulfide (1T-TaS2). Introducing tilt-series ultrafast nanobeam electron diffraction, we reconstruct charge-density wave rocking curves at high momentum resolution. An intermittent suppression of three-dimensional structural correlations promotes a loss of in-plane translational order caused by a high density of unbound topological defects, characteristic of a hexatic intermediate. Our results demonstrate the merit of tomographic ultrafast structural probing in tracing coupled order parameters, heralding universal nanoscale access to laser-induced dimensionality control in functional heterostructures and devices.
Quantum cascade of correlated phases in trigonally warped bilayer graphene,
Nature 608, 298–302 (2022).
Divergent density of states offers an opportunity to explore a wide variety of correlated electron physics. In the thinnest limit, this has been predicted and verified in the ultraflat bands of magic-angle twisted bilayer graphene1,2,3,4,5, the band touching points of few-layer rhombohedral graphite6,7,8 and the lightly doped rhombohedral trilayer graphene9,10,11. The simpler and seemingly better understood Bernal bilayer graphene is also susceptible to orbital magnetism at charge neutrality7 leading to layer antiferromagnetic states12 or quantum anomalous Hall states13. Here we report the observation of a cascade of correlated phases in the vicinity of electric-field-controlled Lifshitz transitions14,15 and van Hove singularities16 in Bernal bilayer graphene. We provide evidence for the observation of Stoner ferromagnets in the form of half and quarter metals10,11. Furthermore, we identify signatures consistent with a topologically non-trivial Wigner–Hall crystal17 at zero magnetic field and its transition to a trivial Wigner crystal, as well as two correlated metals whose behaviour deviates from that of standard Fermi liquids. Our results in this reproducible, tunable, simple system open up new horizons for studying strongly correlated electrons.
Cyanate Formation via Photolytic Splitting of Dinitrogen,
JACS Au 2021, 1, 6, 879–894.
Light-driven N2 cleavage into molecular nitrides is an attractive strategy for synthetic nitrogen fixation. However, suitable platforms are rare. Furthermore, the development of catalytic protocols via this elementary step suffers from poor understanding of N–N photosplitting within dinitrogen complexes, as well as of the thermochemical and kinetic framework for coupled follow-up chemistry. We here present a tungsten pincer platform, which undergoes fully reversible, thermal N2 splitting and reverse nitride coupling, allowing for experimental derivation of thermodynamic and kinetic parameters of the N–N cleavage step. Selective N–N splitting was also obtained photolytically. DFT computations allocate the productive excitations within the {WNNW} core. Transient absorption spectroscopy shows ultrafast repopulation of the electronic ground state. Comparison with ground-state kinetics and resonance Raman data support a pathway for N–N photosplitting via a nonstatistically vibrationally excited ground state that benefits from vibronically coupled structural distortion of the core. Nitride carbonylation and release are demonstrated within a full synthetic cycle for trimethylsilylcyanate formation directly from N2 and CO.
Hydrogen atom collisions with a semiconductor efficiently promote electrons to the conduction band,
Nat. Chem. 15, 326–331 (2023).
The Born–Oppenheimer approximation is the keystone of modern computational chemistry and there is wide interest in understanding under what conditions it remains valid. Hydrogen atom scattering from insulator, semi-metal and metal surfaces has helped provide such information. The approximation is adequate for insulators and for metals it fails, but not severely. Here we present hydrogen atom scattering from a semiconductor surface: Ge(111)c(2 × 8). Experiments show bimodal energy-loss distributions revealing two channels. Molecular dynamics trajectories within the Born–Oppenheimer approximation reproduce one channel quantitatively. The second channel transfers much more energy and is absent in simulations. It grows with hydrogen atom incidence energy and exhibits an energy-loss onset equal to the Ge surface bandgap. This leads us to conclude that hydrogen atom collisions at the surface of a semiconductor are capable of promoting electrons from the valence to the conduction band with high efficiency. Our current understanding fails to explain these observations.
CRC Retreat 2025 - Winterschool in Riezlern
The final CRC Retreat took place from Febuary 23rd to 27th, 2025 at the Marburger Haus in Riezlern. The three-day program offered exciting talks on project progress, as well as lively poster sessions and team building social activities.
IRTG Workshop at DESY
The PhD students from the CRC spend three days at DESY in Hamburg. Many thanks to everybody who helped organizing the workshop and for giving our PhD students an exciting insight into the research at DESY.
2nd International Workshop on Correlated Dynamics in Energy Conversion
Thanks to everybody who participated in making the 2nd International Workshop on Correlated Dynamics in Energy Conversion a success! We hope you had a pleasant and stimulating time for scientific exchange and discussion. more
