arXiv subjects

Henning Sirringhaus

Publications and source records attributed to Henning Sirringhaus.

At least 19 recordsLinked to original sources

arXiv2026

Controlling the growth of 2D conjugated coordination polymers to induce metallic and spin-dependent transport signatures

Understanding growth evolution and thereby implementing precise microstructural tuning of two-dimensional (2D) conjugated coordination polymers (cCPs) is crucial to achieve efficient electronic conduction towards their full potential and to observe materials' intrinsic properties. However, fundamental understanding of how 2D cCPs films grow remains very limited. Here, we use copper-benzenehexathiol (Cu-BHT) cCP as a model system to unravel the growth evolution of layered films in liquid-liquid interfacial synthesis in order to identify strategies to achieve tuning of structure-property relationships. We find that thin films formed at the early stage of growth in 20 minutes facilitate smoother, denser, and horizontally oriented films, and thereby achieve higher electrical conductivity of > 3000 S/cm with a metallic temperature dependence down to 20 K. They also reveal signatures of quantum interference mediated weak antilocalisation and Kondo-like effect in magnetotransport at low temperatures. These phenomena are not observed when long reaction time was employed. Our findings offer a new perspective for the growth of dynamically reversible self-assemblies, that is different from the traditional paradigm of longer reaction time being associated with higher ordering and performance, and offer a platform to study spin-related transport properties of these materials with higher performance for advanced electronic, thermoelectric, and potential spintronic applications.

cond-mat.mtrl-sci↗

arXiv2026

Unbounded Systematic Error in Thin Film Conductivity Measurements

Electrical conductivity is the most fundamental charge transport parameter, and measurements of conductivity are a basic part of materials characterization for nearly all conducting materials. In thin films, conductivity is often measured in four bar architectures in which the current source and voltage measurement are spatially separated to eliminate systematic error due to contact resistance. Despite the apparent simplicity of these measurements, we demonstrate here that the four bar architecture is subject to significant systematic error arising from the finite conductivity of the metal electrodes. Remarkably, these systematic errors can in some cases become unbounded, producing arbitrarily high measured conductivity at modest true film conductivities, within the range relevant to emerging thin film thermoelectric materials such as conducting polymers. These unbounded errors, which can occur even in properly conducted four-point measurements of patterned films, likely explain literature reports of extremely high conductivities in conducting polymers, and can lead to anomalous scaling in temperature dependent studies, potentially leading to incorrect interpretation of the relevant charge transport mechanism. We characterize the device geometric factors that control these errors, which stand partially at odds with those required for accurate Seebeck coefficient measurements. Our analyses allow us to identify device architectures that provide small systematic errors for conductivity and Seebeck coefficient while still providing a low measurement resistance, critical to reducing noise in thermal voltage measurements. These findings provide important guidelines for accurate measurements in the growing field of thin-film thermoelectric materials.

cond-mat.mtrl-sci↗

arXiv2025

RF-Squad: A radiofrequency simulator for quantum dot arrays

Spins in semiconductor quantum dots offer a scalable approach to quantum computing; however, precise control and efficient readout of large quantum dot arrays remain challenging, mainly due to the hyperdimensional voltage space required for tuning multiple gates per dot. To automate this process, large datasets are required for testing and training autotuning algorithms. To address the demand for such large datasets, we introduce RF-Squad, a physics-based simulator designed to realistically replicate radiofrequency (RF) reflectometry measurements of quantum dot arrays, with the ability to go beyond the Constant Interaction Model (CIM) and simulate physical phenomena such as tunnel coupling, tunnel rates, and quantum confinement. Implemented in JAX, an accelerated linear algebra library, RF-Squad achieves high computational speed, enabling the simulation of a 100x100 pixel charge stability diagram of a double quantum dot (DQD) in 52.1 $\pm$0.2 milliseconds at the CIM level. Using optimization algorithms, combined with it's layered architecture, RF-Squad allows users to balance physical accuracy with computational speed, scaling from simple to highly detailed models.

cond-mat.mes-hall↗

arXiv2025

Visualizing Nanodomain Superlattices in Halide Perovskites Giving Picosecond Quantum Transients

The high optoelectronic quality of halide perovskites lends them to be utilized in optoelectronic devices and recently in emerging quantum emission applications. Advancements in perovskite nanomaterials have led to the discovery of processes in which luminescence decay times are sub-100 picoseconds, stimulating the exploration of even faster radiative rates for advanced quantum applications, which have only been prominently realised in III-V materials grown through costly epitaxial growth methods. Here, we discovered ultrafast quantum transients of time scales ~2 picoseconds at low temperature in bulk formamidinium lead iodide films grown through scalable solution or vapour approaches. Using a multimodal strategy, combining ultrafast spectroscopy, optical and electron microscopy, we show that these transients originate from quantum tunnelling in nanodomain superlattices. The outcome of the transient decays, photoluminescence, mirrors the photoabsorption of the states, with an ultra-narrow linewidth at low temperature as low as <2 nm (~4 meV). Localized correlation of the emission and structure reveals that the nanodomain superlattices are formed by alternating ordered layers of corner sharing and face sharing octahedra. This discovery opens new applications leveraging intrinsic quantum properties and demonstrates powerful multimodal approaches for quantum investigations.

cond-mat.mtrl-sci↗

arXiv2024

Critical assessment of contact resistance and mobility in tin perovskite semiconductors

Recent reports highlight the potential of tin-based perovskite semiconductors for high-performance p-type field-effect transistors (FETs) with mobilities exceeding 20 cm2V-1s-1. However, these high mobilities--often obtained via two-probe (2P) methods on devices with small channel length-to-width ratios (L/W < 0.5) operating in the saturation regime at high drain-source currents--raise concerns about overestimation due to contact resistance and non-ideal FET characteristics. Here, we performed gated four-point probe (4PP) FET measurements on Hall bar devices (L/W = 6) of Cs0.15FA0.85SnI3, obtaining a consistent mobility of 3.3 cm2V-1s-1. Upon comparing these with gated 2P measurements of narrow-channel FETs (L/W = 0.1) on the same chip, we resolved the contact resistance (R_C). The 2P linear mobility is underestimated due to voltage drops across R_C, while the 2P saturation mobility is overestimated because of high (dR_C)/(dV_G) near the threshold. Contact resistance effects become more pronounced at lower temperatures. Contact-corrected four-point-probe (4PP) mobilities are independent of bias conditions and are observed to flatten at temperatures lower than 180 K. Future reports of perovskite FET mobilities should include gated 4PP measurements and use devices with larger L/W ratios to minimize nonidealities arising from contact resistance effects.

physics.app-ph↗

arXiv2024

Defect-tolerant electron and defect-sensitive phonon transport in quasi-2D conjugated coordination polymers

Thermoelectric materials, enabling direct waste-heat to electricity conversion, need to be highly electrically conducting while simultaneously thermally insulating. This is fundamentally challenging since electrical and thermal conduction are usually coupled. Here, we discover that quasi-2D conjugated coordination polymer films exhibit this ideal mix of antithetical properties due to coexistence of defect-tolerant charge transport and defect-sensitive heat propagation. The former is highlighted by the highest conductivities > 2000 S cm-1 with metallic temperature dependence observed in disordered films with paracrystallinity > 10%, while the latter manifests in low, temperature-activated lattice thermal conductivities (< 0.38 W m-1 K-1) originating from small-amplitude, quasi-harmonic lattice dynamics with disorder-limited lifetimes and vibrational scattering length on the order of interatomic spacing. Based on temperature-dependent thermoelectric and magnetotransport experiments we identify a two-carrier (hole-electron), ambipolar metallic transport regime as the origin of relatively small Seebeck coefficients in these materials. Our findings identify conjugated coordination polymers as attractive materials for applications in thermoelectric energy harvesting, (bio)electronics and energy storage.

cond-mat.mtrl-sci↗

arXiv2024

Thermoelectric transport in molecular crystals driven by gradients of thermal electronic disorder

Thermoelectric materials convert a temperature gradient into a voltage. This phenomenon is relatively well understood for inorganic materials, but much less so for organic semiconductors (OSs). These materials present a challenge because the strong thermal fluctuations of electronic coupling between the molecules result in partially delocalized charge carriers that cannot be treated with traditional theories for thermoelectricity. Here we develop a novel quantum dynamical simulation approach revealing in atomistic detail how the charge carrier wavefunction moves along a temperature gradient in an organic molecular crystal. We find that the wavefunction propagates from hot to cold in agreement with experiment and we obtain a Seebeck coefficient in good agreement with values obtained from experimental measurements that are also reported in this work. Detailed analysis of the dynamics reveals that the directional charge carrier motion is due to the gradient in thermal electronic disorder, more specifically in the spatial gradient of thermal fluctuations of electronic couplings. It causes an increase in the density of thermally accessible electronic states, the delocalization of states and the non-adiabatic coupling between states with decreasing temperature. As a result, the carrier wavefunction transitions with higher probability to a neighbouring electronic state towards the cold side compared to the hot side generating a thermoelectric current. Our dynamical perspective of thermoelectricity suggests that the temperature dependence of electronic disorder plays an important role in determining the magnitude of the Seebeck coefficient in this class of materials, opening new avenues for design of OSs with improved Seebeck coefficients.

cond-mat.mtrl-sci↗

arXiv2024

Controllable bipolaron formation unveiling structural features of trap states in organic charge transport

Magnetic resonance methods offer a unique chance for in-depth study of conductive organic material systems, not only accounts for number of charge carriers, but also allows manipulations of spin dynamics of particles. Here we present a study of continuous-wave electrically detected magnetic resonance on a range of organic conjugate polymers under transistor architecture, with tunability in both carrier concentration and drifting electric field. We demonstrate the general existence of bipolaron between mobile and trapped charges at the magnetic resonance condition, then estimates the wavefunction expansion of charge carriers on their hopping sites along conductive pathways. This finding allows direct observation of energetically disordered trap sites under the charge hopping picture, linking-up the microscopic structural properties to the bulk electronic performances.

physics.app-ph↗

arXiv2024

Detection of spin pumping free of rectification and thermal artefacts in molecular-based ferromagnetic insulator V[TCNE]x~2

The molecular-based ferrimagnetic insulator V(TCNE)x has gained recent interest for efficient spin-wave excitation due to its low Gilbert damping ratio a=4E-5, and narrow ferromagnetic resonance linewidth f=1Oe. Here we report a clean spin pumping signal detected on V(TCNE)x/metal bilayer structures, free from spin rectification or thermal artifacts. On-chip coupling of microwave power is achieved via a coplanar waveguide to measure the in-plane angle-dependence of the inverse spin-Hall effect under ferromagnetic resonance conditions with respect to a constant external magnetic field. A signature of pure spin current from V(TCNE)x is observed in both platinum and permalloy metal layers, demonstrating the utility of V(TCNE)x for magnon spintronics studies in molecule/solid-state heterostructures.

cond-mat.mtrl-sci↗

arXiv2023

JISA: A Polymorphic Test-and-Measurement Automation Library

JISA is a software library, written in Java, aimed at providing an easy, flexible and standardised means of creating experimental control software for physical sciences researchers. Specifically, with an emphasis on enabling measurement code to be written in an instrument-agnostic way, allowing such routines to be reused across multiple different setups without requiring modification. Additionally, it provides a simple means of recording and handling data, as well as pre-built graphical user interface (GUI) "blocks" to enable the relatively easy creation of graphical control systems. Together these allow users to quickly piece together test-and-measurement programs with coherent user interfaces, without requiring much experience of such things.

physics.ins-det↗

arXiv2023

Fast near-infrared photodetectors based on nontoxic and solution-processable AgBiS2

Solution-processable near-infrared (NIR) photodetectors are urgently needed for a wide range of next-generation electronics, including sensors, optical communications and bioimaging. However, there is currently a compromise between low toxicity and slow (<300 kHz cut-off frequency) organic materials versus faster detectors (>300 kHz cut-off frequency) based on compounds containing toxic lead or cadmium. Herein, we circumvent this trade-off by developing solution-processed AgBiS2 photodetectors with high cut-off frequencies under both white light (>1 MHz) and NIR (approaching 500 kHz) illumination. These high cut-off frequencies are due to the short transit distances of charge-carriers in the AgBiS2 photodetectors, which arise from the strong light absorption of these materials, such that film thicknesses well below 120 nm are adequate to absorb >65% of near-infrared to visible light. By finely controlling the thickness of the photoactive layer, we can modulate the charge-collection efficiency, achieve low dark current densities, and minimize the effects of ion migration to realize fast photodetectors that are stable in air. These outstanding characteristics enable real-time heartbeat sensors based on NIR AgBiS2 photodetectors. # equal contribution, * corresponding authors

cond-mat.mtrl-sci↗

arXiv2023

Tailoring Interlayer Charge Transfer Dynamics in 2D Perovskites with Electroactive Spacer Molecules

The family of hybrid organic-inorganic lead-halide perovskites are the subject of intense interest for optoelectronic applications, from light-emitting diodes to photovoltaics to X-ray detectors. Due to the inert nature of most organic molecules, the inorganic sublattice generally dominates the electronic structure and therefore optoelectronic properties of perovskites. Here, we use optically and electronically active carbazole-based Cz-Ci molecules, where Ci indicates an alkylammonium chain and i indicates the number of CH2 units in the chain, varying from 3-5, as cations in the 2D perovskite structure. By investigating the photophysics and charge transport characteristics of (Cz-Ci)2PbI4, we demonstrate a tunable electronic coupling between the inorganic lead-halide and organic layers. The strongest interlayer electronic coupling was found for (Cz-C3)2PbI4, where photothermal deflection spectroscopy results remarkably demonstrate an organic-inorganic charge transfer state. Ultrafast transient absorption spectroscopy measurements demonstrate ultrafast hole transfer from the photoexcited lead-halide layer to the Cz-Ci molecules, the efficiency of which increases by varying the chain length from i=5 to i=3. The charge transfer results in long-lived carriers (10-100 ns) and quenched emission, in stark contrast with the fast (sub-ns) and efficient radiative decay of bound excitons in the more conventional 2D perovskite (PEA)2PbI4, in which phenylethylammonium (PEA) acts as an inert spacer. Electrical charge transport measurements further support enhanced interlayer coupling, showing increased out-of-plane carrier mobility from i=5 to i=3. This study paves the way for the rational design of 2D perovskites with combined inorganic-organic electronic proper-ties through the wide range of functionalities available in the world of organics.

physics.app-ph↗

arXiv2023

Revealing contributions to conduction from transport within ordered and disordered regions in highly doped conjugated polymers through analysis of temperature-dependent Hall measurements

Hall effect measurements in doped polymer semiconductors are widely reported, but are difficult to interpret due to screening of Hall voltages by carriers undergoing incoherent transport. Here, we propose a refined analysis for such Hall measurements, based on measuring the Hall coefficient as a function of temperature, and modelling carriers as existing in a regime of variable "deflectability" (i.e. how strongly they "feel" the magnetic part of the Lorentz force). By linearly interpolating each carrier between the extremes of no deflection and full deflection, we demonstrate that it is possible to extract the (time-averaged) concentration of deflectable charge carriers, $\left $, the average, temperature-dependent mobility of those carriers, $\left<μ_d\right>(T)$, as well as the ratio of conductivity that comes from such deflectable transport, $d(T)$. Our method was enabled by the construction of an improved AC Hall measurement system, as well as an improved data extraction method. We measured Hall bar devices of ion-exchange doped films of PBTTT-C$_{14}$ from 10--300 K. Our analysis provides evidence for the proportion of conductivity arising from deflectable transport, $d(T)$, increasing with doping level, ranging between 15.4% and 16.4% at room temperature. When compared to total charge-carrier-density estimates from independent methods, the values of $\left $ extracted suggest that carriers spend $\sim$37% of their time of flight being deflectable in the most highly doped of the devices measured here. The extracted values of $d(T)$ being less than half this value thus suggest that the limiting factor for conductivity in such highly doped devices is carrier mobility, rather than concentration.

cond-mat.mtrl-sci↗

arXiv2022

Charge Transport in Mixed Metal Halide Perovskite Semiconductors

Investigation of the inherent field-driven charge transport behaviour of 3D lead halide perovskites has largely remained a challenging task, owing primarily to undesirable ionic migration effects near room temperature. In addition, the presence of methylammonium in many high performing 3D perovskite compositions introduces additional instabilities, which limit reliable room temperature optoelectronic device operation. Here, we address both these challenges and demonstrate that field-effect transistors (FETs) based on methylammonium-free, mixed-metal (Pb/Sn) perovskite compositions, that are widely studied for solar cell and light-emitting diode applications, do not suffer from ion migration effects as their pure Pb counterparts and reliably exhibit hysteresis free p-type transport with high mobility reaching 5.4 $cm^2/Vs$, ON/OFF ratio approaching $10^6$, and normalized channel conductance of 3 S/m. The reduced ion migration is also manifested in an activated temperature dependence of the field-effect mobility with low activation energy, which reflects a significant density of shallow electronic defects. We visualize the suppressed in-plane ionic migration in Sn-containing perovskites compared to their pure-Pb counterparts using photoluminescence microscopy under bias and demonstrate promising voltage and current-stress device operational stabilities. Our work establishes FETs as an excellent platform for providing fundamental insights into the doping, defect and charge transport physics of mixed-metal halide perovskite semiconductors to advance their applications in optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2021

Structural and dynamic disorder, not ionic trapping, controls charge transport in highly doped conducting polymers

Doped organic semiconductors are critical to emerging device applications, including thermoelectrics, bioelectronics, and neuromorphic computing devices. It is commonly assumed that low conductivities in these materials result primarily from charge trapping by the Coulomb potentials of the dopant counter-ions. Here, we present a combined experimental and theoretical study rebutting this belief. Using a newly developed doping technique, we find the conductivity of several classes of high-mobility conjugated polymers to be strongly correlated with paracrystalline disorder but poorly correlated with ionic size, suggesting that Coulomb traps do not limit transport. A general model for interacting electrons in highly doped polymers is proposed and carefully parameterized against atomistic calculations, enabling the calculation of electrical conductivity within the framework of transient localisation theory. Theoretical calculations are in excellent agreement with experimental data, providing insights into the disordered-limited nature of charge transport and suggesting new strategies to further improve conductivities.

cond-mat.mtrl-sci↗

arXiv2021

Distinguishing spin pumping from spin rectification in organic semiconductor-based lateral spin pumping device architectures

Over the last two decades organic spintronics has developed into a striving field with exciting reports of long spin diffusion lengths and spin relaxation times in organic semiconductors (OSCs). Easily processed and inexpensive, OSCs are considered a potential alternative to inorganic materials for use in spintronic applications. Spin currents have been detected in a wide range of materials, however, there is still uncertainty over the origin of the signals. Recently, we explored spin transport through an organic semiconductor with lateral spin injection and detection architectures, where the injected spin current is detected non-locally via spin-to-charge conversion in an inorganic detector. In this work we show that the widely-used control experiments like linear power dependence and inversion of the signal with the magnetic field are not sufficient evidence of spin transport and can lead to an incorrect interpretation of the signal. Here, we use in-plane angular dependent measurements to separate pure spin signal from parasitic effects arising from spin rectification (SREs). Apart from well established anisotropic magnetoresistance (AMR) and anomalous Hall effect (AHE), we observed a novel effect which we call spurious inverse spin Hall effect (ISHE). It strongly resembles ISHE behaviour, but arises in the ferromagnet rather than the detector meaning this additional effect has to be considered in future work.

cond-mat.mes-hall↗

arXiv2021

Room-temperature optically detected magnetic resonance of single defects in hexagonal boron nitride

Optically addressable spins in materials are important platforms for quantum technologies, such as repeaters and sensors. Identification of such systems in two-dimensional (2d) layered materials offers advantages over their bulk counterparts, as their reduced dimensionality enables more feasible on-chip integration into devices. Here, we report optically detected magnetic resonance (ODMR) from previously identified carbon-related defects in 2d hexagonal boron nitride (hBN). We show that single-defect ODMR contrast can be as strong as 6% and displays a magnetic-field dependence with both positive or negative sign per defect. This bipolarity can shed light into low contrast reported recently for ensemble ODMR measurements for these defects. Further, the ODMR lineshape comprises a doublet resonance, suggesting either low zero-field splitting or hyperfine coupling. Our results offer a promising route towards realising a room-temperature spin-photon quantum interface in hexagonal boron nitride.

cond-mat.mes-hall↗

arXiv2020

Tuning Spin Current Injection at Ferromagnet/Non-Magnet Interfaces by Molecular Design

There is a growing interest in utilizing the distinctive material properties of organic semiconductors for spintronic applications. Here, we explore injection of pure spin current from Permalloy into a small molecule system based on dinaphtho[2,3-b:2,3-f]thieno[3,2-b]thiophene (DNTT) at ferromagnetic resonance. The unique tunability of organic materials by molecular design allows us to study the impact of interfacial properties on the spin injection efficiency systematically. We show that both, spin injection efficiency at the interface as well as the spin diffusion length can be tuned sensitively by the interfacial molecular structure and side chain substitution of the molecule.

physics.app-ph↗