Optoelectronic Materials Research Articles

(Invited) Comprehensive Analysis of Exciton Diffusion with Time-Resolved Fluorescence Spectroscopy, Anisotropy and Imaging

Excitons produced in materials play a crucial role in photo-energy conversion such as photovoltaics and electroluminescence devices. The temporal and spatial diffusion of excitons is a key factor for dominating the fundamental performance of optoelectronic materials. In this context, analysis of the exciton diffusion dynamics is an important issue for obtaining the rational design of the materials. Excitons diffusing in materials can be characterized by several parameters such as the energy level, orientation of the transition dipole moment and spatial distribution, and the detection of these properties is required for the comprehensive analysis. In the present study, we show time-resolved fluorescence methods for detecting the above relevant properties of excitons.First, time-resolved fluorescence spectroscopy is a basic technique for analyzing the exciton diffusion dynamics. Fluorescence intensity is detected as functions of observation wavelength and time, and the spectral intensity and shift of fluorescence bands provide information on the population of excitons and their energy level. For example, dynamic Stokes shift indicates downhill energy migration and excitons are trapped by the defective site in molecular aggregates. Second, fluorescence anisotropy can be a good indicator for tracking the exciton diffusion in amorphous materials. Fluorescence anisotropy is sensitive to orientation change in transition dipole moments (TDMs) between absorption and fluorescence. In systems where the relative orientation of adjacent molecules is different from each other, such as amorphous solids, the exciton diffusion is accompanied with the change in TDM. Thus, appropriate modeling of molecular alignment enables quantitative estimation of the exciton diffusion coefficient and diffusion length from the anisotropy signal. Finally, time-resolved imaging is a combination of time-resolved spectroscopy and super-resolution microscopy, and an emergent technique for visualizing real-space propagation of excitons in materials. The diffraction-limited excitation beam produces excitons in several hundreds of nanometers and the subsequent exciton diffusion is evaluated by the spatial width of the fluorescence spot. The temporal broadening of the fluorescence spot directly reflects the exciton distribution and we can intuitively obtain the diffusion coefficient and length. Unlike the conventional methods for bulk materials, the advantage of the time-resolved imaging is the applicability to materials with nano- and meso-scale heterogeneous structure and it enables site-selective evaluation of the exciton transport capability. In the conference site, we will also show the application of the above methods to supramolecular polymers and thermally activated delayed fluorescence materials. Figure 1

Liquid phase exfoliation of few-layer borophene with high hole mobility for low-power electronic devices

Borophene, the two-dimensional allotrope of boron, has garnered significant interest in recent years due to its exceptional electronic, mechanical, and optical properties. In this work, an environment-friendly green approach has been utilized to synthesize p-type borophene, which consists of few layers as evidenced by electron and atomic force microscopic images. The Raman analysis indicated that these borophene layers possess β12 and χ3 phases. The photoemission spectra of these samples exhibit single exponential decay with a long lifetime of 7.2 µsec, showcasing its potential as a phosphorescent material in optoelectronics and quantum technologies. The photo-sensing capability of borophene was investigated by fabricating a Si/SiO2/Borophene/Ti/Pt photo-detector, which achieved an external quantum efficiency of 31 %, maximum photo responsivity of 200 mAW−1 and detectivity of 8.7x1011 Jones. Hall effect van der Pauw measurements revealed the p-type conductivity of the borophene film, along with a high hole mobility of 931.44 cm2V-1s−1 and a charge carrier density of 2 x 1012 cm−3, rendering these layers suitable for high-speed and low power electronic devices. This work emphasizes the importance of novel 2D materials like borophene with exceptional optoelectronic characteristics for developing future low-power electronic devices with remarkable performance.

New phthalocyanine-hybrid glass materials for optoelectronics – Photostability and temperature-dependent optical properties

The organically modified silicate matrix (ORMOSIL) is the most commonly used solution for immobilization of the optically active organic compounds. The materials are characterized by much higher thermal and chemical resistance. The aim of the study was to obtain the hybrid material (in the form of thin films and gels) using the sol-gel method with covalently bound newly synthesized d-block metal phthalocyanine. The hybrid layers were prepared using the dip-coating technique. A series of the sol-gel syntheses based on various types of silicate matrix modifiers (trialkoxysilanes) and their molar ratios were prepared to obtain a photostable and durable material. The optical properties of phthalocyanine (fluorescence) with different concentration in the hybrid glass matrix were studied. Thermoluminescence of the hybrid materials were analyzed. Finally, tests of material stability under the exposure of UV at room temperature and additional under high-energy radiation were carried out with emission measurement in the ultraviolet range and in the temperature range 298–573K.

Single Crystal Ruddlesden-Popper and Dion-Jacobson Metal Halide Perovskites for Visible Light Photodetectors: Present Status and Future Perspectives.

2D metal halide perovskites (MHPs), mainly the studied Ruddlesden-Popper (RP) and Dion-Jacobson (DJ) phases, have gained enormous popularity as optoelectronic materials owing to their self-assembled multiple quantum well structures, tunable semiconducting properties, and improved structural stability compared to their bulk 3D counterparts. The performance of polycrystalline thin film devices is limited due to the formation of defects and trap states. However, as studied so far, single crystal-based devices can provide a better platform to improve device performance and investigate their fundamental properties more reliably. This Review provides the first comprehensive report on the emerging field of RP and DJ perovskite single crystals and their use in visible light photodetectors of varied device configurations. This Review structurally summarizes the 2D MHP single crystal growth methods and the parameters that control the crystal growth process. In addition, the characterization techniques used to investigate their crystal properties are discussed. The review further provides detailed insights into the working mechanisms as well as the operational performance of 2D MHP single crystal photodetector devices. In the end, to outline the present status and future directions, this Review provides a forward-looking perspective concerning the technical challenges and bottlenecks associated with the developing field of RP and DJ perovskite single crystals. Therefore, this timely review will provide a detailed overview of the fast-growing field of 2D MHP single crystal-based photodetectors as well as ignite new concepts for a wide range of applications including solar cells, photocatalysts, solar H2 production, neuromorphic bioelectronics, memory devices, etc.

Deep Blue CsPbBr3 Quantum Wires with Tailored Shapes.

Low-dimension metal halide perovskites are attractive for bandgap tunable optoelectronic materials. Among them, 1-D CsPbBr3 quantum wires (QWs) are emerging as promising deep-blue luminescent material. However, the growth dynamics of 1-D perovskite QWs are intricate, making the study and control of 1-D QWs highly challenging. In this study, a strategy for controlling both the length and width of the CsPbBr3 QWs was realized. The temperature-dependent isotropic growth mechanism was revealed and employed as the main tool for the oriented growth of 1-D CsPbBr3 QWs for various aspect ratios. Our results pave the way for the controlled synthesis of ultrasmall perovskite nanocrystals.

Tuning the electronic structure of monolayer MoS2 towards metal like via vanadium doping

Doping of two-dimensional layered semiconducting materials is becoming pivotal in tailoring their electronic properties, enabling the development of advanced electronic and optoelectronic devices, where the selection of dopant is important. Here, we demonstrate the potential of substitutional vanadium (V) doping in monolayer molybdenum disulfide (MoS2) lattice in different extents leading to tunable electronic and optoelectronic properties. We found that low-level V doping (∼1 at.%) induces p-type characteristics in otherwise n-type monolayer MoS2, whereas medium-level doping (∼5 at.%) leads to an ambipolar semiconductor. Degenerately doped MoS2 (∼9 at.%) facilitates a transition from semiconducting towards metallic (metal-like) with reduced electrical resistivity (∼4.5 Ωm of MoS2 to ∼2.2×10−5Ωm), low activation energy for transport (∼11 meV), and electric field independent drain current in field effect transistor–based transfer characteristics. A detailed temperature- and power-dependent photoluminescence study along with density functional theory–based calculations in support unravels the emergence of an excitonic transition at ∼850 nm with its intensity dependent on the amount of vanadium. This study shows the potential of V doping in MoS2 for generating multifunctional two-dimensional materials for next generation electronics, optoelectronics, and interconnects with systematic control over its electronic structure in a wide range. Published by the American Physical Society 2024

Enhanced UV Nonlinear Optical Properties in Layered Germanous Phosphites through Functional Group Sequential Construction

AbstractThis study pioneers a novel strategy for synthesizing solar‐blind ultraviolet (UV) nonlinear optical (NLO) crystals through functional groups sequential construction, effectively addressing the inherent trade‐offs among broad transmittance, enhanced second‐harmonic generation (SHG), and optimal birefringence. We have developed two innovative van der Waals layered germanous phosphites: GeHPO3, the first Ge(II)‐based oxide NLO crystal which exhibits a black phosphorus‐like structure, and K(GeHPO3)2Br, distinguished by its exceptional birefringence and graphene‐like structure. Significantly, GeHPO3 exhibits a remarkable array of NLO properties, including the highest SHG coefficient recorded among all NLO crystals for phase‐matching and generating 266 nm coherent light via quadruple frequency conversion. It delivers a potent SHG intensity, surpassing KH2PO4 (KDP) by 10.3 times at 1064 nm and β‐BaB2O4 by 1.3 times at 532 nm, complemented by a distinct UV absorption edge at 211 nm and moderate birefringence of 0.062 at 546 nm. Comprehensive theoretical analysis links these exceptional characteristics to the unique NLO‐active GeO34− units and the distinctive, highly ordered layered structures. Our findings deliver essential experimental insights into the development of Ge(II)‐based optoelectronic materials and present a strategic blueprint for engineering structure‐driven functional materials with customized properties.

Quantum chemical package Jaguar: A survey of recent developments and unique features.

This paper is dedicated to the quantum chemical package Jaguar, which is commercial software developed and distributed by Schrödinger, Inc. We discuss Jaguar's scientific features that are relevant to chemical research as well as describe those aspects of the program that are pertinent to the user interface, the organization of the computer code, and its maintenance and testing. Among the scientific topics that feature prominently in this paper are the quantum chemical methods grounded in the pseudospectral approach. A number of multistep workflows dependent on Jaguar are covered: prediction of protonation equilibria in aqueous solutions (particularly calculations of tautomeric stability and pKa), reactivity predictions based on automated transition state search, assembly of Boltzmann-averaged spectra such as vibrational and electronic circular dichroism, as well as nuclear magnetic resonance. Discussed also are quantum chemical calculations that are oriented toward materials science applications, in particular, prediction of properties of optoelectronic materials and organic semiconductors, and molecular catalyst design. The topic of treatment of conformations inevitably comes up in real world research projects and is considered as part of all the workflows mentioned above. In addition, we examine the role of machine learning methods in quantum chemical calculations performed by Jaguar, from auxiliary functions that return the approximate calculation runtime in a user interface, to prediction of actual molecular properties. The current work is second in a series of reviews of Jaguar, the first having been published more than ten years ago. Thus, this paper serves as a rare milestone on the path that is being traversed by Jaguar's development in more than thirty years of its existence.

Enhanced UV Nonlinear Optical Properties in Layered Germanous Phosphites through Functional Group Sequential Construction.

This study pioneers a novel strategy for synthesizing solar-blind ultraviolet (UV) nonlinear optical (NLO) crystals through functional groups sequential construction, effectively addressing the inherent trade-offs among broad transmittance, enhanced second-harmonic generation (SHG), and optimal birefringence. We have developed two innovative van der Waals layered germanous phosphites: GeHPO3, the first Ge(II)-based oxide NLO crystal which exhibits a black phosphorus-like structure, and K(GeHPO3)2Br, distinguished by its exceptional birefringence and graphene-like structure. Significantly, GeHPO3 exhibits a remarkable array of NLO properties, including the highest SHG coefficient recorded among all NLO crystals for phase-matching and generating 266 nm coherent light via quadruple frequency conversion. It delivers a potent SHG intensity, surpassing KH2PO4 (KDP) by 10.3 times at 1064 nm and β-BaB2O4 by 1.3 times at 532 nm, complemented by a distinct UV absorption edge at 211 nm and moderate birefringence of 0.062 at 546 nm. Comprehensive theoretical analysis links these exceptional characteristics to the unique NLO-active GeO3 4- units and the distinctive, highly ordered layered structures. Our findings deliver essential experimental insights into the development of Ge(II)-based optoelectronic materials and present a strategic blueprint for engineering structure-driven functional materials with customized properties.

Influence of Bi2O3, PbO, and Y2O3 nanofillers on the physical features of polyvinyl chloride: materials for optoelectronics or dielectric applications

Influence of Bi2O3, PbO, and Y2O3 nanofillers on the physical features of polyvinyl chloride: materials for optoelectronics or dielectric applications

Tunability of Sb2Se3 phase change material for multi-domain optoelectronics

Phase change materials play an essential role in the development of tuneable optics by overcoming the limitations possessed by conventional optics due to their static behaviour. Due to their non-volatile nature, chalcogenide materials attained attention beyond other phase change materials. Antimony-based chalcogenides are promising due to low absorption loss, optimal refractive index change, and compatibility with silicon integration. This study optimises near-stoichiometric sputtered Sb2Se3 thin films and investigates their compositional, physical, and optical properties change by thermal, optical, and electrical stimuli. We further extend the investigation to the induced intermediate states in the Sb2Se3 thin film for multi-bit operation for tunable photonics and phase-change memory with a current switching ratio of 104 during a phase transition. The findings are integral to the realisation of high-capacity optical switches and routers, displays with larger colour distribution, and photonic memories with high computational capabilities.

Advancement in Synthetic Strategies of Phosphorus Heterocycles: Recent Progress from Synthesis to Emerging Class of Optoelectronic Materials.

Organophosphorus heterocycles have long been acknowledged for their significant potential across diverse fields, including catalysis, material science, and drug development. Incorporating phosphorus functionalities into organic compounds offers a means to effectively tailor their medicinal properties, augment biological responses, and enhance selectivity and bioavailability. The distinctive physical and photoelectric characteristics of phosphorus-containing conjugated compounds have garnered considerable interest as promising materials for organic optoelectronics. These compounds find extensive utility in various applications such as light-emitting diodes, photovoltaic cells, phosphole-based fluorophores, and semiconductors.

Effect of Mg/Ag co–doping on crystal structure, optical, and transport properties of SnO2 compound

The attempt to search for novel materials for optoelectronics material has become a highly debated and intensively investigated field of study. Within the scope of this investigation, Sn0.94Ag0.06-xMgxO2 (0 ≤ x ≤ 0.06) polycrystalline samples were produced using the traditional solid–state reaction method, and their crystalline structure, micro–structure, Raman spectroscopy, optical, and transport characteristics were investigated. Confirmation of a single rutile phase with a tetragonal crystal structure through XRD (X–ray diffraction) analysis is revealed. The morphology study by scanning electron microscopy indicated the formation of nanometric grains. All elements are evenly distributed throughout the structure, as seen by the elemental color mapping. The successful incorporation of Mg/Ag to the SnO2 lattice is evidenced by two prominent peaks in the Raman spectra of these compounds, with wavenumbers of 634 and 775 cm−1, which correspond to the A1g and B2g Raman modes, respectively. The UV–Vis spectrophotometer facilitated the acquisition of absorbance and transmittance data, which revealed that the optical band gap exhibited an expansion when the quantity of Mg/Ag co–doping increased in the SnO2 material. The transmittance value was also shown to increase from 80 % to 90 % with increased Mg co–doping concentration. The Maxwell–Weigner model has been employed to fully understand how the dielectric constant (εr), loss tangent (tan δ), complex impedance, and ac conductivity of Mg/Ag co–doped SnO2 compounds behave depending on frequency. The current–voltage (I–V) characteristics of the sample were measured using a Keithley 6517b electrometer in two–probe mode with a Tin metal pressure contact. The properties of I–V exhibited an Ohmic behavior. A study on the room temperature resistivity reveled that the materials are highly resistive in the nature.

Structural phase transition and optical properties of zero-dimensional cobalt bromide hybrid material

Zero-Dimensional (0D) metal halide materials have recently emerged as a class of potential optoelectronic materials because of the structural diversity and superior photophysical properties. Here we report a 0D cobalt bromide hybrid material, [Br(CH2)3NH3]2CoBr4 (BPA-CoBr4, BPA=Br(CH2)3NH3, 3-Bromopropylamine), in which the isolated metal halide tetrahedron (CoBr42-) is completely separated each other and surrounded by the organic ligand Br(CH2)3NH3+. Differential scanning calorimetry (DSC) measurements exhibit BPA-CoBr4 undergoes a first-order structural phase transition, as clearly visible to a pair of weak peaks at 340 K (heating) and 317 K (cooling). Single crystal X-ray diffractions were carried out at 293 K and 360 K to explain the phase transformation mechanism, indicating it is an isostructural order–disorder type. The crystal structures which both crystalize in a monoclinic P21/c crystal symmetry and the most distinct difference between room-temperature and high-temperature structures is the order–disorder transition of the 3-Bromopropylamine, which is the driving force of the phase transition. The UV–vis absorption spectra reveal that BPA-CoBr4 has a steep absorption edge at 280 nm corresponding to photo energy of 4.4 eV. The density functional theory (DFT) calculations were performed to study the electronic structure with narrower indirect bandgap 3.9 eV which is lower than the experimental values. PDOS plots show that the electronic states of Co-d and Br-p orbitals are mainly contributed for the VBM and CBM of BPA-CoBr4.

Polymer Materials for Optoelectronics and Energy Applications.

This review comprehensively addresses the developments and applications of polymer materials in optoelectronics. Especially, this review introduces how the materials absorb, emit, and transfer charges, including the exciton-vibrational coupling, nonradiative and radiative processes, Förster Resonance Energy Transfer (FRET), and energy dynamics. Furthermore, it outlines charge trapping and recombination in the materials and draws the corresponding practical implications. The following section focuses on the practical application of organic materials in optoelectronics devices and highlights the detailed structure, operational principle, and performance metrics of organic photovoltaic cells (OPVs), organic light-emitting diodes (OLEDs), organic photodetectors, and organic transistors in detail. Finally, this study underscores the transformative impact of organic materials on the evolution of optoelectronics, providing a comprehensive understanding of their properties, mechanisms, and diverse applications that contribute to advancing innovative technologies in the field.

Advancements and challenges in strained group-IV-based optoelectronic materials stressed by ion beam treatment

In this perspective article, we discuss the application of ion implantation to manipulate strain (by either neutralizing or inducing compressive or tensile states) in suspended thin films. Emphasizing the pressing need for a high-mobility silicon-compatible transistor or a direct bandgap group-IV semiconductor that is compatible with complementary metal–oxide–semiconductor technology, we underscore the distinctive features of different methods of ion beam-induced alteration of material morphology. The article examines the precautions needed during experimental procedures and data analysis and explores routes for potential scalable adoption by the semiconductor industry. Finally, we briefly discuss how this highly controllable strain-inducing technique can facilitate enhanced manipulation of impurity-based spin quantum bits (qubits).

Effect of partial cation substitution on optoelectronic properties and ion diffusion behavior of inorganic lead halide perovskite: A theoretical investigation

Cation substitution is a widely utilized approach for tailoring the properties of lead halide perovskites. A comprehensive understanding of the impact of various cation substitutions on optoelectronic properties and ion diffusion behavior is crucial for enhancing the performance of halide perovskite materials. In this study, we constructed various double halide perovskites by cation substitution and investigated their optoelectronic properties and ion diffusion behavior through first-principles calculations. Our findings reveal that the A-site substitution with alkali cation Rb does not significantly influence the optoelectronic properties of lead halide perovskites. However, it will boost the halide migration due to the enlarged migration bottleneck. The B-site substitution with alkali earth element Sr significantly suppresses the halide migration; while the material will be no longer suitable for visible light absorption due to the enlarged bandgap. The substitution of Pb with d-orbital fulfilled Zn can also suppress the halide migration, but it will give rise to an indirect bandgap and hence affect the optoelectronic performance. The substitution of Pb with Sn can enhance both the thermostability and optoelectronic performance owing to the smaller ionic radius and similar ns2-containing electronic configuration. The increased migration barrier indicates that ion diffusion is also inhibited in double perovskite Cs2SnPbI6. Our results imply that the optoelectronic properties can be further optimized by tuning the ratio of Sn/Pb or the thickness of the perovskite layer in photovoltaic device. These results would be useful guide for the development of novel lead-less optoelectronic perovskite materials.

Enhancing blue light excitation in Pb-free double perovskites by decreasing the energy barrier of the self-trapping exciton and prospects for environment-friendly optoelectronic applications

In Pb-free double perovskites (DPs) optoelectronic material systems, the energy barrier ∆Eb suppression between free excitons (FEs) and self-trapped excitons (STEs) makes it difficult to achieve blue-light excitation even as the bandgap narrows, which has become a major challenge in the development of full-colour displays, lighting, optoelectronics and catalytic technologies. Here, Cs2-aKaAg0.6Na0.4In0.8Bi0.2Cl6-x-yBrx(SH)y DPs, prepared by doping with HS- (hydrosulfide ion), Br- and K+, achieve a blue excitation at 468 nm. The octahedral tilt caused by doping with K+, Br- and HS- ions reduces the local crystal dimensions and thus the energy barrier ∆Eb. The aggregation of electrons around the AgX6 octahedron under the action of HS- contributes to the formation of effective STE emission under blue light excitation. Furthermore, the potential impact of blue-light-excited Cs2-aKaAg0.6Na0.4In0.8Bi0.2Cl6-x-yBrx(SH)y DPs on enhancing the power conversion efficiency (PCE) of photovoltaic modules and the photodegradation efficiency of Rhodamine B (RhB) is explored. The study concludes by highlighting the wide-ranging applications in displays, photovoltaics, and photocatalytic degradation that could be realized through the utilization of blue-light-excited Pb-free DPs.

Photoelectrochemical analysis of Pb2+ based on Au@PTCA Schottky junction with Pb2+-G quadruplex structure.

Herein, a novel photoelectrochemical (PEC) aptasensor using gold nanoparticles@3,4,9,10-perylene tetracarboxylic (Au@PTCA) Schottky junction as the effective optoelectronic material and lead ion (Pb2+)-G quadruplex structure as the efficient quencher was constructed for the detection of Pb2+ with high sensitivity and excellent selectivity. Au@PTCA Schottky junction, which was proposed by the in situ reduction of Au NPs on the PTCA surface, exhibited a strong unidirectional conductivity, which could generate a significantly enhanced PEC signal compared with the pure PTCA. The Pb2+-G quadruplex structure with a large spatial hindrance effect was formed when the target Pb2+ was present owing to the occurrence of the specific recognition between Pb2+ and its aptamer S1. The formation of a Pb2+-G quadruplex structure effectively quenched the initial signal generated by the Au@PTCA Schottky junction, which was derived from restricted electron transport and light transmission. The obtained prominently decreased PEC signal could achieve the quantitative detection of Pb2+ from 0.5 pM to 500 nM, with a low detection limit of 0.17 pM. The preparation time of this PEC aptasensor was 13 h, and the time for PEC measurement depended on the illumination time, which switched off-on-off for 10 s-20 s-10 s. The study proposed here with high sensitivity and excellent selectivity for Pb2+ analysis offered a novel and reliable tool for environmental monitoring related to heavy metal ions.

Prediction of Frequency-Dependent Optical Spectrum for Solid Materials: A Multioutput and Multifidelity Machine Learning Approach.

The frequency-dependent optical spectrum is pivotal for a broad range of applications from material characterization to optoelectronics and energy harvesting. Data-driven surrogate models, trained on density functional theory (DFT) data, have effectively alleviated the scalability limitations of DFT while preserving its chemical accuracy, expediting material discovery. However, prevailing machine learning (ML) efforts often focus on scalar properties such as the band gap, overlooking the complexities of optical spectra. In this work, we employ deep graph neural networks (GNNs) to predict the frequency-dependent complex-valued dielectric function across the infrared, visible, and ultraviolet spectra directly from the crystal structures. We explore multiple architectures for the spectral multioutput representation of the dielectric function and utilize various multifidelity learning strategies, such as transfer learning and fidelity embedding, to address the challenges associated with the scarcity of high-fidelity DFT data. Additionally, we model key solar cell absorption efficiency metrics, demonstrating that learning these parameters is enhanced when integrated through a learning bias within the learning of the frequency-dependent absorption coefficient. This study demonstrates that leveraging multioutput and multifidelity ML techniques enables accurate predictions of optical spectra from crystal structures, providing a versatile tool for rapidly screening materials for optoelectronics, optical sensing, and solar energy applications across an extensive frequency spectrum.