Light Matter Interactions in Energy Materials

Kick Group

We develop state-of-the-art electronic structure methods, and build new ones where existing approaches fall short, to describe light–matter interactions in complex, realistic materials. Our focus spans energy materials, quantum light sources, and quantum information platforms, united by a common challenge: the excited-state physics that determines device function occurs far from equilibrium, on femtosecond timescales and nanometer length scales, in systems that are large, correlated, and structurally complex.

The central difficulty is methodological. Methods that correctly capture correlated many-body physics are confined to small, idealized systems. Methods that reach experimentally relevant scales sacrifice precisely the physics that real materials demand. Our research programme is built around closing this gap: developing the theoretical and computational capabilities to describe excited states in large, realistic systems from first principles, at a cost that makes the relevant length and time scales tractable.

The physical phenomena we target are inherently complex. Excitonic states, quantum confinement, electron localization, charge carrier dynamics, and spin degrees of freedom are all crucial to material performance. Competing processes such as non-radiative decay must be suppressed with high efficiency to prevent device degradation. By studying prototypical compounds with both established and novel methods, we build atomistic understanding of these mechanisms and use it to inform the design of materials with superior properties. Our materials focus spans two interconnected problems. In perovskite solar cells and nanocrystals, we study carrier cooling, quantum cutting, and exciton self-trapping: how hot carriers thermalise after photon absorption, how energy is redistributed across coupled electronic and phononic degrees of freedom, how quantum cutting can convert a single high-energy photon into multiple usable excitations, and how excitons can localize on ultrafast timescales through strong coupling to lattice distortions. These processes sit at the heart of the efficiency limits that determine whether perovskite devices can fulfill their commercial promise, and understanding them requires simultaneously capturing correlated carrier dynamics and structural complexity, a challenge that most existing approaches cannot meet.

Another and growing direction is the theory of solar-batteries: devices that absorb sunlight and store the resulting charge directly at the nanoscale, without external solar cells or separate storage components. This would collapse the conventional light-harvesting and energy storage chain into a single material. The theoretical challenge is substantial, as charge storage must compete with fast non-radiative decay, and the relevant physics spans photon absorption, exciton dissociation, carrier localization, and electrochemical storage, all within one system. We are beginning to build the computational framework needed to describe this full chain from first principles.

The second focus of our group is the development of computational methods for excited-state phenomena in large and realistic systems. As system size grows, from molecules to quantum dots, nanoplatelets, and surface-adsorbed chromophores, the number of relevant excited states grows rapidly, and standard methods become prohibitively expensive long before the physically interesting regime is reached. We develop hierarchical approximation schemes that make this challenge tractable, targeting the relevant states directly rather than exhaustively computing the full spectrum. Alongside these large-scale methods, we use wavefunction-based approaches to investigate non-radiative decay pathways in detail. In materials where strong electron-phonon coupling drives fast carrier relaxation, as in the soft lattices of perovskites or the confined modes of nanocrystals, an accurate description of how electronic and nuclear degrees of freedom are coupled is essential. These methods give us direct access to the quantum mechanical mechanisms behind carrier cooling, trap-assisted recombination, and other decay channels that determine whether energy is usefully harvested or lost. Together, these two methodological directions are complementary: one scales our reach to realistic system sizes, the other deepens our physical understanding where the correlated physics is most demanding.

Methods:

Density Functional Theory
Time-Dependent Density Functional Theory
Self-Interaction Correction Methods
Model Hamiltonians
Machine-Learning Techniques

Selected Publications

Selected recent publications are listed below (a full list can be found under Publications):

Advancing our Understanding of Optoionic Effects for the Design of Solar Batteries: A Theoretical Perspective, M. Rinaldi, M. Kick, K. Reuter, C. Carbogno, Journal of Physics: Materials (2025)

Band Alignment in Core–Shell Nanocrystals by Estimating Wave Function Tunneling Probabilities, M. Kick, E Alexander, T. Van Voorhis, Nano Letters (2025)

Super-resolution Techniques to Simulate Electronic Spectra of Large Molecular Systems, M. Kick, E. Alexander, A. Beiersdorfer, T. Van Voorhis, Nature Communications - editor highlight (2024) 

Understanding Trap States in InP and GaP Quantum Dots through Density Functional Theory, E. Alexander, M. Kick, T. Van Voorhis, Nano Letters (2024)

A-Site Cation Influence on the Structural and Optical Evolution of Ultrathin Lead Halide Perovskite Nanoplatelets, C. J. Krajewska, et al., ACS Nano (2024)

Synthesis of Zwitterionic CsPbBr₃ Nanocrystals with Controlled Anisotropy using Surface‐Selective Ligand Pairs, H. Zhu, et al., Advanced Materials (2023)

Mobile Small Polarons Qualitatively Explain Conductivity in Lithium Titanium Oxide Battery Electrodes, M. Kick, C. Grosu, M. Schuderer, C. Scheurer, H. Oberhofer, The Journal of Physical Chemistry Letters (2020)

Intricacies of DFT+ U, not only in a Numeric Atom Centered Orbital Framework, M. Kick, K. Reuter, H. Oberhofer, Journal of Chemical Theory and Computation (2019)