arXiv subjects

Felix Deschler

Publications and source records attributed to Felix Deschler.

9 recordsLinked to original sources

arXiv2026

Composition Anisotropy Drives Large Bulk Photovoltaic Fields Along the Non-polar Vertical Direction in 2D Hybrid Perovskite Ferroelectrics

The photovoltaic electric field of the bulk photovoltaic effect (BPE) reflects the intrinsic ability of ferroelectrics to separate photoexcited excitons into electrons and holes, and are essential parameters for applications such as voltage-readout photodetectors. Because polarization defines the cation-anion displacement and noncentrosymmetric axis, the polar direction is generally one of the orientations exhibiting strong bulk photovoltaic field (EBPE). Here, we report emergent BPE behavior in 2D hybrid perovskite ferroelectrics (HPFs), where EBPE can be two orders of magnitude higher along the vertical nonpolar direction than along the polar in-plane direction. Its magnitude is up to orders of magnitude higher than that of benchmark photoferroelectrics across different material systems and is the highest among 2D HPFs reported so far. This strong BPE response with emergent directional anisotropy originates from the unique coupling among the shift-current BPE mechanism, an efficient photocarrier-generating inorganic part, and an insulator-like organic part, a combination that is conflicting or inaccessible in traditional photoferroelectrics. This composition and anisotropy also produce basic BPE behavior distinct from that of typical photoferroelectrics, including a laser intensity dependent photovoltage and a nonlinear scaling of photovoltage with material dimension. We analyze and develop a series of formulas to describe the emergent photovoltage phenomena, which should be applicable to this novel 2D ferroelectrics family and to polar systems with similar anisotropy and robust photoelectric response.

cond-mat.mtrl-sci↗

arXiv2025

Ultrafast light-induced formation of a metastable hidden state in bismuth vanadate

Bismuth vanadate (BiVO$_4$) is a key photocatalyst for solar fuel applications, yet fundamental questions remain regarding the nature of photogenerated polaronic states and the lattice dynamics that govern its light-to-chemical pathways. Here, we use femtosecond optical pump-X-ray probe measurements to track the photoinduced electronic and structural dynamics in BiVO$_4$ across multiple length and time scales. Transient X-ray absorption spectroscopy captures sub-picosecond electron localization within VO$_4$ tetrahedra, consistent with small polaron formation, whereas time-resolved X-ray diffraction reveals a slower, multi-picosecond lattice reorganization into a hidden photoexcited state that is structurally distinct from both the monoclinic ground state and the high-temperature tetragonal phase. Supported by density functional theory, we show that hole-lattice interactions dynamically reduce the ground state monoclinic distortion, stabilizing the hidden state. Our results demonstrate that electron- and hole-lattice coupling jointly shape the excited state landscape, with implications for carrier transport, interfacial energetics, and light-to-chemical energy conversion pathways.

cond-mat.mtrl-sci↗

arXiv2025

FRET-Enhanced Singlet Fission in Pentacene Derivatives

Conversion of solar energy with high quantum efficiencies is a key challenge in energy technologies. Excitation energy transfer (EET) mechanisms, such as F\"orster resonance energy transfer (FRET), play a crucial role in facilitating minimal energy loss in biological light-harvesting systems by directing excitation energy to conversion centers. Inspired by this, we show that singlet fission (SF) sensitizers are multi-exciton generation centers, to which surrounding molecules funnel excitation energy via FRET. We study the impact of such EET on SF using two structurally distinct yet optically similar pentacene derivatives: a stability-enhanced ''Gel\"ander'' pentacene, and the well-studied TIPS-pentacene. Transient absorption spectroscopy reveals a $R^{6}$ dependence of the SF rate on molecular separation $R$ in binary acene:polymethylmetacrylate thin film blends, which is typical for FRET. Optimizing FRET is a promising direction for future improvements in light harvesting using SF materials, inspired by natural light-harvesting complexes.

cond-mat.mtrl-sci↗

arXiv2024

Light-induced optical orientation of magnetic moments in transition-metal doped hybrid metal halide perovskites

Using optical orientation to manipulate magnetic moments in matter with light is a key objective in opto-spintronics, however, realizations of such control on ultrafast timescales are limited. Here, we report ultrafast optical control of magnetic moment orientation in magnetically doped metal halide perovskites. Employing intense pulses of circularly polarized light, we inject populations of spin-polarized charge carriers in pristine and manganese-doped MAPbBr3 thin films. Using transient Faraday rotation spectroscopy, we probe the ultrafast magnetic moment dynamics following photoexcitation and find that light-induced magnetization in doped samples is increased by a factor of 10. We attribute this to photoexcited carriers acting on the magnetic moments of manganese dopant-ions via the sp-d exchange interaction, which forces them to align on picosecond timescales. Our findings open new avenues for device structures that use hybrid metal halide perovskites for ultrafast optical manipulation and read-out of magnetic order with the potential for high switching rates.

physics.app-ph↗

arXiv2023

Solution-processed NiPS3 thin films from Liquid Exfoliated Inks with Long-Lived Spin-Entangled Excitons

Antiferromagnets are promising materials for future opto-spintronic applications since they show spin dynamics in the THz range and no net magnetization. Recently, layered van der Waals (vdW) antiferromagnets have been reported, which combine low-dimensional excitonic properties with complex spin-structure. While various methods for the fabrication of vdW 2D crystals exist, formation of large area and continuous thin films is challenging because of either limited scalability, synthetic complexity, or low opto-spintronic quality of the final material. Here, we fabricate centimeter-scale thin films of the van der Waals 2D antiferromagnetic material NiPS3, which we prepare using a crystal ink made from liquid phase exfoliation (LPE). We perform statistical atomic force microscopy (AFM) and scanning electron microscopy (SEM) to characterize and control the lateral size and number of layers through this ink-based fabrication. Using ultrafast optical spectroscopy at cryogenic temperatures, we resolve the dynamics of photoexcited excitons. We find antiferromagnetic spin arrangement and spin-entangled Zhang-Rice multiplet excitons with lifetimes in the nanosecond range, as well as ultranarrow emission linewidths, despite the disordered nature of our films. Thus, our findings demonstrate scalable thin-film fabrication of high-quality NiPS3, which is crucial for translating this 2D antiferromagnetic material into spintronic and nanoscale memory devices and further exploring its complex spin-light coupled states.

physics.chem-ph↗

arXiv2020

Magnetic proximity effect on excitonic spin states in Mn-doped layered hybrid perovskites

Materials combining the optoelectronic functionalities of semiconductors with control of the spin degree of freedom are highly sought after for the advancement of quantum technology devices. Here, we report the paramagnetic Ruddlesden-Popper hybrid perovskite Mn:(PEA)2PbI4 (PEA = phenethylammonium) in which the interaction of isolated Mn2+ ions with magnetically brightened excitons leads to circularly polarized photoluminescence. Using a combination of superconducting quantum interference device (SQUID) magnetometry and magneto-optical experiments, we find that the Brillouin-shaped polarization curve of the photoluminescence follows the magnetization of the material. This indicates coupling between localized manganese magnetic moments and exciton spins via a magnetic proximity effect. The saturation polarization of 15% at 4 K and 6 T indicates a highly imbalanced spin population and demonstrates that manganese doping enables efficient control of excitonic spin states in Ruddlesden-Popper perovskites. Our finding constitutes the first example of polarization control in magnetically doped hybrid perovskites and will stimulate research on this highly tuneable material platform that promises tailored interactions between magnetic moments and electronic states.

cond-mat.mtrl-sci↗

arXiv2020

Mechanism of carrier localization in doped perovskite nanocrystals for bright emission

Nanocrystals based on metal-halide perovskites offer a promising material platform for highly efficient lighting. Using transient optical spectroscopy, we study excitation recombination dynamics in manganese-doped CsPb(Cl,Br)3 perovskite nanocrystals. We find an increase in the intrinsic excitonic radiative recombination rate upon doping, which is typically a challenging material property to tailor. Supported by ab initio calculations, we can attribute the enhanced emission rates to increased exciton localization through lattice periodicity breaking from Mn dopants, which increases exciton effective masses and overlap of electron and hole wavefunctions and thus the oscillator strength. Our report of a fundamental strategy for improving luminescence efficiencies in perovskite nanocrystals will be valuable for maximizing efficiencies in light-emitting applications.

cond-mat.mtrl-sci↗

arXiv2017

Ultrafast carrier thermalization in lead iodide perovskite probed with two-dimensional electronic spectroscopy

In band-like semiconductors, charge carriers form a thermal energy distribution rapidly after optical excitation. In hybrid lead halide perovskites, the cooling of such thermal carrier distributions occurs on timescales of ~300 fs via carrier-phonon scattering. However, the initial build-up of the thermal distribution proved difficult to resolve with pump-probe techniques due to the requirement of high resolution, both in time and in energy. Here, we use two-dimensional electronic spectroscopy with sub-10fs resolution to directly observe the carrier interactions that lead to the formation of 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. We extract characteristic carrier thermalization times from below 10 fs to 85 fs. These values allow for mobilities of up to 500 cm^2 V^(-1) s^(-1) at carrier densities lower than 2x10^19 cm^(-3) and limit the time for carrier extraction in hot carrier solar cells.

cond-mat.mtrl-sci↗

arXiv2016

Spinodal Decomposition-Enabled Halide Perovskite Double Heterostructure with Reduced Fröhlich Electron-Phonon Coupling

Epitaxial III-V semiconductor heterostructures are key components in modern microelectronics, electro-optics and optoelectronics. With superior semiconducting properties, halide perovskite materials are rising as promising candidates for coherent heterostructure devices. In this report, spinodal decomposition is proposed and experimentally implemented to produce epitaxial double heterostructures in halide perovskite system. Pristine epitaxial mixed halide perovskites rods and films were synthesized via Van der Waals epitaxy by chemical vapor deposition method. At room temperature, photon was applied as a knob to regulate the kinetics of spinodal decomposition and classic coarsening. By this approach, halide perovskite double heterostructures were created carrying epitaxial interfaces and outstanding optical properties. Reduced Fröhlich electron-phonon coupling was discovered in coherent halide double heterostructure, which is hypothetically attributed to the classic phonon confinement effect widely existing in III-V double heterostructures. The ability to develop coherent double heterostructures in halide perovskites paves an avenue to exploring halide perovskite-based quantum wells and superlattices for high-performance and low-cost optoelectronics, electro-optics and microelectronics.

cond-mat.mtrl-sci↗