Organic solar cells (OSCs) have attracted much interest in recent years for their unique properties such as flexibility, light weight and the low cost and ease of their fabrication processes. While not destined to replace silicon- based technology, organic based solar cells provide a promising technology for wearables, windows, as well as light weight constructions that cannot hold the current massive PV modules. A lot of research has been devoted to the development of modern organic materials for solar cell devices. The development of modern and highly effective non-fullerene accepting materials has achieved great progress in organic solar cells’ (OSCs’) performance reaching a stage where device design strategies must be addressed for further enhancement. A previous work done by our group[1] presents a device engineering approach to enhance the OPVs’ performance using modulation-doping of the hole Extraction layer (HEL). A planer heterojunction device was investigated using two well-studied standard materials 1,1-bis [(di-4-tolylamino) phenyl] cyclohexane (TAPC) as a hole transporting material, C70 as the accepting material and P-type dopants, C60F48. The dopants were induced in a ẟ -doped layer of 10 nm width within the TAPC layer. The presence of the doped layer within the device induces an internal electric field at the junction leading to enhanced charge separation efficiency, reaching 50% enhancement in the current at the maximum power point and 30% at 0.8Voc. To extend the applicability of the design to cells based on modern materials produced through solution processing and make it universal to (almost) any donor-acceptor pair, we developed a strategy based on a cross-linkable high band-gap polymer matrix[2] where the donor material of choice can be blended at ~20w% to serve as the charge transporting/extracting material.[3] Being insoluble it can be considered as part of the substrate and the flexibility in choosing the transport material makes it universal. with the cooperation of a Korean research group, we also examined a thermally cross-linkable material that is highly conductive for holes which will serve not just as a host matrix for dopants, but also as a hole transporting material. We will first describe the general properties of the enhanced charge-extraction structure utilizing Poly (vinyl carbazole) bearing cinnamate pendants (PVK-cin [50%]) as the x-linkable matrix, Poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine (PTAA) as the transport/extraction material, and C60F48 doped PTAA as the δ-doped layer, we will also describe the properties of an HEL based on the thermally cross-linkable hole transport material X-TPACz with C60F48 doped X-TPACz as a δ-doped layer. [4] Next, we describe the properties of a complete cell that is based on PBDB-T-2F (PM6) and Y6 (BTP-4F) as the donor-acceptor pair, respectively.[5, 6] We also examine the effect of using magnesium; a low work function metal an interlayer on the performance of the cell. To place the experimental results in perspective, we conduct detailed device simulation and compare the experimentally measured enhancement to the maximum theoretical prediction.

In Mott materials strong electron correlation yields a spectrum of complex electronic structures. Recent synthesis advancements open realistic opportunities for harnessing Mott physics to design transformative devices. However, a major bottleneck in realizing such devices remains the lack of control over the electron correlation strength. This stems from the complexity of the electronic structure, which often veils the basic mechanisms underlying the correlation strength. Here, we present control of the correlation strength by tuning the degree of orbital overlap using picometer-scale lattice engineering. We illustrate how bandwidth control and concurrent symmetry breaking can govern the electronic structure of a correlated $SrVO_3$ model system. We show how tensile and compressive biaxial strain oppositely affect the $SrVO_3$ in-plane and out-of-plane orbital occupancy, resulting in the partial alleviation of the orbital degeneracy. We derive and explain the spectral weight redistribution under strain and illustrate how high tensile strain drives the system towards a Mott insulating state. Implementation of such concepts will enable to harness correlated electron phenomena towards new solid state devices and circuits. These findings pave the way for understanding and controlling electron correlation in a broad range of functional materials, driving this powerful resource for novel electronics closer towards practical realization.

Doped heavy metal-free III – V semiconductor nanocrystal quantum dots are of great interest both from the fundamental aspects of doping in highly confined structures, and from the applicative side of utilizing such building blocks in the fabrication of p-n homojunction devices. InAs nanocrystals, that are of particular relevance for short wave IR detection and emission applications, manifest heavy n-type character poising a challenge for their transition to p-type behavior. We present p-type doping of InAs nanocrystals with Zn – enabling control over the charge carrier type in InAs QDs field effect transistors. The post-synthesis doping reaction mechanism is studied for Zn precursors with varying reactivity. Successful p-type doping was achieved by the more reactive precursor, diethylzinc. Substitutional doping by Zn²⁺ replacing In³⁺ is established by X-ray absorption spectroscopy analysis. Furthermore, enhanced near IR photoluminescence is observed due to surface passivation by Zn as indicated from elemental mapping utilizing high resolution electron microscopy corroborated by X-ray photoelectron spectroscopy study. The demonstrated ability to control the carrier type, along with the improved emission characteristics, paves the way towards fabrication of optoelectronic devices active in the short wave IR region utilizing heavy-metal free nanocrystal building blocks.

This article is protected by copyright. All rights reserved

We present a comprehensive study of the temperature dependent electronic and optoelectronic properties of a tunnelling injection quantum dot laser. The optical power-voltage ( P opt – V ) characteristics are shown to be correlated with the current-voltage ( I – V ) and capacitance-voltage ( C – V ) dependencies at low and elevated temperatures. Cryogenic temperature measurements reveal a clear signature of resonant tunnelling manifested in periodic responses of the I – V and P opt – V characteristics, which diminish above 60 K. The C – V characteristics reveal a hysteresis stemming from charging and de-charging of the quantum dots, as well as negative capacitance. The latter is accompanied by a clear peak that appears at the voltage corresponding to carrier clamping, since the clamping induces a transient-like effect on the carrier density. C – V measurements lead also to a determination of the dot density which is found to be similar to that obtained from atomic force microscopy. C – V measurements enable also to extract the average number of trapped electrons in each quantum dot which is 0.95. As the important parameters of the laser have signatures in the electrical and electro-optical characteristics, the combination serves as a powerful tool to study intricate details of the laser operation.

Transport of excitons and charge carriers in molecular systems can be enhanced by coherent coupling to photons, giving rise to the formation of hybrid excitations known as polaritons. Such enhancement has far-reaching technological implications; however, the enhancement mechanism and the transport nature of these hybrid excitations remain elusive. Here we map the ultrafast spatiotemporal dynamics of polaritons formed by mixing surface-bound optical waves with Frenkel excitons in a self-assembled molecular layer, resolving polariton dynamics in energy/momentum space. We find that the interplay between the molecular disorder and long-range correlations induced by coherent mixing with light leads to a mobility transition between diffusive and ballistic transport, which can be controlled by varying the light–matter composition of the polaritons. Furthermore, we show that coupling to light enhances the diffusion coefficient of molecular excitons by six orders of magnitude and even leads to ballistic flow at two-thirds the speed of light.

For over 80 years of research, the conventional description of free-electron radiation phenomena, such as Cherenkov radiation, has remained unchanged: classical three-dimensional electromagnetic waves. Interestingly, in reduced dimensionality, the properties of free-electron radiation are predicted to fundamentally change. Here, we present the first observation of Cherenkov surface waves, wherein free electrons emit narrow-bandwidth photonic quasiparticles propagating in two dimensions. The low dimensionality and narrow bandwidth of the effect enable us to identify quantized emission events through electron energy loss spectroscopy. Our results support the recent theoretical prediction that free electrons do not always emit classical light and can instead become entangled with the photons they emit. The two-dimensional Cherenkov interaction achieves quantum coupling strengths over 2 orders of magnitude larger than ever reported, reaching the single-electron–single-photon interaction regime for the first time with free electrons. Our findings pave the way to previously unexplored phenomena in free-electron quantum optics, facilitating bright, free-electron-based quantum emitters of heralded Fock states.

Heterostructures based on two dimensional (2D) materials offer the possibility to achieve synergistic functionalities which otherwise remain secluded by their individual counterparts. Herein ferroelectric polarization switching in alpha-In2Se3 has been utilized to engineer multilevel non-volatile conduction states in partially overlapping alpha-In2Se3-MoS2 based ferroelectric semiconducting field effect device. In particular, we demonstrate how the intercoupled ferroelectric nature of alpha-In2Se3 allows to non-volatilely switch between n-i and n-i-n type junction configurations based on a novel edge state actuation mechanism, paving the way for sub-nanometric scale non-volatile device miniaturization. Furthermore the induced asymmetric polarization enables enhanced photogenerated carriers separation resulting in extremely high photoresponse of 1275 AW-1 in the visible range and strong non-volatile modulation of the bright A- and B- excitonic emission channels in the overlaying MoS2 monolayer. Our results show significant potential to harness the switchable polarization in partially overlapping alpha-In2Se3-MoS2 based FeFETs to engineer multimodal non-volatile nanoscale electronic and optoelectronic devices.

Many scientific and technological applications make use of strong microwave fields. These are often realized in conjunction with microwave resonators that have small geometric features in which such fields are generated. For example, in magnetic resonance, large microwave and RF magnetic fields make it possible to achieve fast control over the measured electron or nuclear spins in the sample and to detect them with high sensitivity. The numerical analysis of resonators with small geometric features can pose a significant challenge. This paper describes a general method of analysis and characterization of surface microresonators in the context of electron spin resonance (ESR) spectroscopy and spin-based quantum technology. Our analysis is based on the Electric Field Integral Equation (EFIE) and the Poggio-Miller-Chang-Harrington-Wu-Tsai (PMCHWT) formulation. In particular, we focus on a class of resonator configurations that possesses extremely small subwavelength features, which normally would require an ultra-fine mesh. We present several efficient techniques to numerically model, solve, and analyze these types of configurations for both normal and superconducting structures. The validation of these techniques is established both numerically and experimentally by the S11 parameters as well as the provision of direct mapping of the resonator’s microwave magnetic field component using a unique electron spin resonance micro-imaging method.

With antimicrobial resistance becoming a major threat to healthcare settings around the world, there is a paramount need for rapid point-of-care antimicrobial susceptibility testing (AST) diagnostics. Unfortunately, most currently available clinical AST tools are lengthy, laborious, or are simply inappropriate for point-of-care testing. Herein, we design a 3D-printed microfluidic gradient generator that automatically produces two-fold dilution series of clinically relevant antimicrobials. We first establish the compatibility of these generators for classical AST (i.e., broth microdilution) and then extend their application to include a complete on-chip label-free and phenotypic AST. This is accomplished by the integration of photonic silicon chips, which provide a preferential surface for microbial colonization and allow optical tracking of bacterial behavior and growth at a solid–liquid interface in real-time by phase shift reflectometric interference spectroscopic measurements (PRISM). Using Escherichia coli and ciprofloxacin as a model pathogen-drug combination, we successfully determine the minimum inhibitory concentration within less than 90 minutes. This gradient generator-based PRISM assay provides an integrated AST device that is viable for convenient point-of-care testing and offers a promising and most importantly, rapid alternative to current clinical practices, which extend to 8–24 h.

Nuclear magnetic resonance (NMR) spectroscopy provides atomic-level molecular structural information.  However, in molecules containing unpaired electron spins, NMR signals are difficult to measure directly.  In such cases, data is obtained using the electron-nuclear double resonance (ENDOR) method, where nuclei are detected through their interaction with nearby unpaired electron spins.  Unfortunately, electron spins spread the ENDOR signals, which challenges current acquisition techniques, often resulting in low spectral resolution that provides limited structural details.  Here, we show that by using miniature microwave resonators to detect a small number of electron spins, integrated with miniature NMR coils, one can excite and detect a wide bandwidth of ENDOR data in a single pulse.  This facilitates the measurement of ENDOR spectra with narrow lines spread over a large frequency range at much better spectral resolution than conventional approaches, which helps reveal details of the paramagnetic molecules’ chemical structure that were not accessible before.