Optoelectronic Conversion Research Articles

Long-distance transport of hot carriers due to acoustic phonon bottleneck in PbSe with room-temperature sensitive mid-infrared sensing

In the optoelectronic conversion process of semiconductors, the photo-excited carriers with energy higher than energy band edge, i.e., hot carriers, have always fast (picoseconds scale) dissipated within 100 nanometers distance through lattice scattering. Specifically, the hot carriers relaxation accounts for more than 60% energy loss in narrow bandgap semiconductor. Herein, we observe an ultralong transport of hot carriers (558 nm) by local light excitation in single-crystalline thermoelectric semiconductor PbSe via the time-resolved reflectivity dynamics. The ultraweak phonon emission of PbSe results in a long-distance thermalized carriers transport due to acoustic phonon bottleneck. Furthermore, the hot carriers effect gives rise to a self-driven (zero bias), fast (900 ns), and sensitive (D* = 1.1 × 1010 cm Hz1/2 W−1 at 3.3 μm) mid-infrared detection and imaging at room temperature. Our discovery provides an insight into optoelectronic conversion mechanism of narrow bandgap thermoelectric semiconductors with intriguing optoelectronic applications.

Fabrication of ZnWO4-SnO2 Core–Shell Nanorods for Enhanced Solar Light-Driven Photoelectrochemical Performance

This article describes the effective synthesis of colloidal SnO2 quantum dots and ZnWO4 nanorods using wet chemical synthesis and hydrothermal synthesis, respectively. The resulting ZnWO4-SnO2 core–shell nanorod heterostructure is then made, and its structural, optical, and morphological properties are assessed using XRD, SEM, TEM, and DRS. The heterojunction’s structural confinement increases the exposure of its reactive sites, and its electronic confinement promotes its redox activity. The heterostructure subsequently exhibits a smaller bandgap and better light-harvesting capabilities, resulting in increased photoelectrochemical performance. The heterostructure of core–shell nanorods shows promise for usage in a range of optoelectronic devices and effective solar energy conversion.

Silicon microring resonator based all-optical 3-input majority gate and its applications

In this study, we propose an all-optical majority gate using silicon waveguide-based microring resonator for the first time to our knowledge. All-optical microring resonator based majority gate has attractive properties such as energy-efficient, ultra-high-speed, and compact which are essential for optical computing. We have designed different logic circuits such as AND, OR, NOR, NAND, and one-bit full adder by exploiting the majority gate with inverter circuits. Optoelectronic conversion which limits the operational speed is avoided in our design. The operational speed of our design is nearly 260 Gbps. The required pump power for switching is only 1.66 mW for micro-ring resonator based switch which is very less comparatively. These designs have been realized in MATLAB as well as in Ansys Lumerical finite difference time domain (FDTD) simulation platform. The "figure of merits" of the presented majority gate is achieved numerically through simulation. The obtained values of extinction ratio and contrast ratio are much higher for the proposed majority gate and the values are 28.11 dB and 32.88 dB, respectively. The on-off ratio is also high for single microring resonator and it is 38.2 dB.

Control and Enhancement of Single-Molecule Electroluminescence through Strong Light–Matter Coupling

The energetic positions of molecular electronic states at molecule/electrode interfaces are crucial factors for determining the transport and optoelectronic properties of molecular junctions. Strong light-matter coupling offers a potential for manipulating these factors, enabling a boost in the efficiency and versatility of these junctions. Here, we investigate electroluminescence from single-molecule junctions in which the molecule is strongly coupled with the vacuum electromagnetic field in a plasmonic nanocavity. We demonstrate an improvement in the electroluminescence efficiency by employing the strong light-matter coupling in conjunction with the characteristic feature of single-molecule junctions to selectively control the formation of the lowest-energy excited state. The mechanism of efficiency improvement is discussed based on the energetic position and composition of the formed polaritonic states. Our findings indicate the possibility to manipulate optoelectronic conversion in molecular junctions by strong light-matter coupling and contribute to providing design principles for developing efficient molecular optoelectronic devices.

Two-dimensional single crystal monoclinic gallium telluride on silicon substrate via transformation of epitaxial hexagonal phase

Van der Waals (vdW) epitaxial growth of large-area and stable two-dimensional (2D) materials of high structural quality on crystalline substrates is crucial for the development of novel device technologies. 2D gallium monochalcogenides with low in-plane symmetry stand out among the layered semiconductor materials family for next-generation optoelectronic and energy conversion applications. Here, we demonstrate the formation of large-area, single crystal and optically active 2D monoclinic gallium telluride (m-GaTe) on silicon substrate via rapid thermal annealing induced phase transformation of vdW epitaxial metastable hexagonal gallium telluride (h-GaTe). Stabilization of multilayer h-GaTe on Si occurs due to the role of the first layer symmetry together with efficient GaTe surface passivation. Moreover, we show that the phase transformation of h-GaTe to m-GaTe is accompanied by the strain relaxation between Si substrate and GaTe. This work opens the way to the fabrication of single-crystal 2D anisotropic semiconductors on standard crystalline wafers that are difficult to be obtained by epitaxial methods.

Editorial for the Special Issue on Advances in Optoelectronic Devices

Optoelectronic devices are fabricated based on an optoelectronic conversion effect, which is a developing research field of modern optoelectronic technology and microelectronics technology [...].

Plasma-assisted gas-phase aggregation of clusters for functional nanomaterials

The application of low-temperature plasma-based methods for the synthesis of functional nanomaterials has been growing for several decades and nanoparticles (NPs) play an increasing role in this effort. NPs have been considered for numerous applications such as optoelectronic energy conversion, electrocatalysis for fuel cells, novel plasmonic materials, electroluminescence, macromolecular self-assembly, supramolecular chemistry, and biomedical applications. The focus of this review will be devoted to NPs prepared by vacuum-based plasma-assisted sources. In the majority of cases, plasma has been excited by a planar magnetron. At first, concisely, the state-of-the-art of plasma-based gas aggregation cluster sources is presented. Then, the stability of the deposition process and enhancement of the production yield as well as tailoring of the composition, structure, and shape of NPs are discussed. In addition, in-flight modification of NPs, the interaction of NPs with a substrate, and deposition onto the liquids are presented.

Thiol-Free Synthesis of Bright Near-Infrared-Emitting Ag2S Nanocrystals through Heterovalent-Metal Decoration for Ecofriendly Solar Cells

Environmentally friendly Ag2S nanocrystals (NCs) show potential applications as light-absorbing semiconductors for thin-film photovoltaics or biological taggants. However, thiol ligands are generally involved during the synthesis of Ag2S NCs to maintain colloidal stability, hindering postexchange of these crystal-bound thiolate ligands. Here, using common non-thiol ligands (oleic acid and oleylamine), we develop a general strategy of surface heterovalent-metal (Bi3+, Ga3+, In3+, Sb3+, and Zn2+) decoration to synthesize colloidal cation-rich Ag2S NCs achieving a high photoluminescence quantum yield up to 22% at ∼1230 nm. Density functional theory calculations reveal the heterovalent-metal cations exhibit stronger orbital coupling to the ligands than Ag atoms, and thus stronger binding affinity, resulting in reduced dynamic surface ligands to produce compact cation-rich Ag2S NCs with high solubility in nonpolar solvents. We further show that surface-decorated Bi atoms can accumulate the electron charge density, leading to surface-related band-edge emissions with increased electron–hole separation and prolonged exciton lifetimes of the Bi-decorated Ag2S NCs, which are desirable for many optoelectronic conversion applications. Using a 40 nm-thick light-absorbing layer of Bi-decorated Ag2S NCs, the optimized solar cells show a short-circuit current density of 18.6 mA cm–2 and a power conversion efficiency of over 4%.

Enhancement of wide-band trace terahertz absorption spectroscopy based on microstructures: a review.

Research on the interaction between nanoscale materials and light holds significant scientific significance for the development of fields such as optoelectronic conversion and biosensing. The study of micro- and nano-optics has produced numerous outstanding research achievements by utilizing the dielectric optical coupling mechanism and plasmon effects to enhance the interaction between light and matter. These findings have demonstrated tremendous potential for applications in the field of molecular fingerprint sensing. This review focuses on a retrospective analysis of recent research studies in the enhancement of wide-band trace terahertz absorption spectroscopy. The physical mechanisms of using waveguide structures, dielectric metasurfaces/meta-gratings, and spoof surface plasmon polaritons (SSPs) to improve the interaction between light and trace-amount matters are introduced. The new approaches and methods for enhancing broad-band terahertz absorption spectroscopy of trace samples using microstructure designs are discussed. Additionally, we elucidate the scientific ideas and exploratory achievements in enhancing terahertz fingerprint spectroscopy detection. Finally, we provide an outlook on the research and development direction and potential practical applications of absorption spectroscopy enhancement detection.

First-principles calculations for comparative band structure study of SrTiO3 perovskite on bulk and layered phases for efficient optoelectronic conversion

A computational investigation over structural, electronic, optical, thermal, thermoelectric and elastic properties of the bulk and layered phases of perovskite compound namely SrTiO3 have been computed using WIEN2K code by means of Full-potential (FP) Linearized Augmented Plane Wave (LAPW) method implemented from DFT (Density Functional Theory) by applying Generalized Gradient Approximations (GGA), Local Density Approximations (LDA), modified Becke Johnson (mBJ) and Spin Orbit Coupling (SOC) computations. Further on this study we made surface structure of this compound by creating a supercell with various distances between the layers and compared their properties with bulk SrTiO3. The layered surfaces of SrTiO3 with varying distances are (i) single top layer (ii) double SrTiO3 layers with 5 a.u. distance (iii) double SrTiO3 layers with 18 a.u. distance have been constructed using the Struct editor program implemented in the WIEN2k code. The structural parameters viz., lattice constant, bond length, bond angles, formation energy, the electronic parameters such as band gap, Density of States (DoS), band structure and optical fundamental constants like dielectric function, optical conductivity, refraction, transmittance, absorbance, resistivity, reflectivity, Phonon dispersion curves and thermal properties such as Debye temperature, entropy, Gibbs free optimized energy (stabled / optimized state), thermoelectric properties such as Seebeck coefficient, Power factor, thermoelectric figure of merit, Pugh's ratio, elastic constants, modulus of elasticity and stiffness matrix have been computed and available results are compared and agreed well with the literature. The SrTiO3 bulk and layered surface exhibits direct band gap located at the Γ symmetry point of the Brillouin zone. From all the above analysis the layered materials with optimum variation of distances (double layers with 5 a.u) are predominantly favorable and efficient than bulk SrTiO3 for optoelectronic devices.

Improved Photo-Excited Carriers Transportation of WS2 -O-Doped-Graphene Heterostructures for Solar Steam Generation.

Two-dimensional (2D) transition metal dichalcogenides and graphene have revealed promising applications in optoelectronic and energy storage and conversion. However, there are rare reports of modifying the light-to-heat transformation via preparing their heterostructures for solar steam generation. In this work, commercial WS2 and sucrose are utilized as precursors to produce 2D WS2 -O-doped-graphene heterostructures (WS2 -O-graphene) for solar water evaporation. The WS2 -O-graphene evaporators demonstrate excellent average water evaporation rate (2.11kgm-2 h-1 ) and energy efficiency (82.2%), which are 1.3- and 1.2-fold higher than WS2 and O-doped graphene-based evaporators, respectively. Furthermore, for the real seawater with different pH values (pH 1 and 12) and rhodamine B pollutants, the WS2 -O-graphene evaporators show great average evaporation rates (≈2.08 and 2.09kgm-2 h-1 , respectively) for producing freshwater with an extremely low-grade of dye residual and nearly neutral pH values. More interestingly, due to the self-storage water ability of WS2 -O-graphene evaporators, water evaporation can be implemented without the presence of bulk water. As a result, the evaporation rate reaches 3.23kgm-2 h-1 , which is ≈1.5 times higher than the regular solar water evaporation system. This work provides a new approach for preparing 2D transition metal dichalcogenides and graphene heterostructures for efficient solar water evaporation.

Discovery of a novel visible-light-active photodetector based on bismuth ferrite: constructing and optimizing the Cr-doped-BiFeO3/NiO thin film heterostructure

Bismuth ferrite (BFO) with narrow bandgap (<2.70 eV) is an uprising star in the application of optoelectronic conversion in visible (Vis) region. Fe-site doping by transition metals is a recognized strategy to reduce leakage current in order to create more qualified BFO-based optoelectronic devices. We aim to constitute the heterostructure of BiFe1-xCrxO3 (BFCO) coupling to hole-transporter NiO, serving as Vis-active photodetector with superior photoresponse speed. The influence of Cr doping ratio on BFCO is systematically investigated, indicating that doping Cr can effectively restrain not only the reduction of Fe3+ state but also the generation of oxygen vacancies. Moreover, by taking advantage of desirable energy-band alignment, BFCO/NiO heterojunction can reach the optimized response time constants of photocurrent rising and decay, i.e., τr and τd are, respectively, lowered down to 0.23 and 0.38 ms, which are almost two order-of-magnitude lower than that of pure-BFO/NiO and also more than one order-of-magnitude lower than that of single-layer BFCO film. It confirms an overwhelming photoresponse performance over other Vis-active counterparts. Herein, we for the first time achieve the Vis photodetector based on BFCO, by virtue of functional interfacial structure of BFCO-NiO to energetically separate photogenerated electron–hole pairs as well as improve charge carrier transportation.

Low phase noise THz generation from a fiber-referenced Kerr microresonator soliton comb

THz oscillators generated via frequency-multiplication of microwaves are facing difficulty in achieving low phase noise. Photonics-based techniques, in which optical two tones are translated to a THz wave through opto-electronic conversion, are promising if the relative phase noise between the two tones is well suppressed. Here, a THz (≈560 GHz) wave with a low phase noise is provided by a frequency-stabilized, dissipative Kerr microresonator soliton comb. The repetition frequency of the comb is stabilized to a long fiber in a two-wavelength delayed self-heterodyne interferometer, significantly reducing the phase noise of the THz wave. A measurement technique to characterize the phase noise of the THz wave beyond the limit of a frequency-multiplied microwave is also demonstrated, showing the superior phase noise of the THz wave to any other photonic THz oscillators (>300 GHz).

МЕТОД ГЕНЕРАЦИИ СВЕРХШИРОКОПОЛОСНЫХ СВЧ-СИГНАЛОВ С ЛИНЕЙНО-ЧАСТОТНОЙ МОДУЛЯЦИЕЙ НА ОСНОВЕ САМОГЕТЕРОДИНИРОВАНИЯ ИЗЛУЧЕНИЯ ЛАЗЕРНОГО ДИОДА

In this paper, microwave photonic technique of ultrawideband linearly frequency modulated signals generation is proposed. The proposed method based on direct modulation of the laser diode current, which provides a periodic change in the emission frequency. The Michelson interferometer summarizes laser signal and its replica with time delay exceeding 10 ms, which, in turn, is defined by time difference between arms. Optoelectronic conversion is performed in high-speed high-power photodiode. The proposed approach makes it possible to generate microwave signals with linear frequency modulation in the frequency range up to several tens of gigahertz by means of laser pump current modulation in the frequency range less than 100 MHz. The method of ultra-wideband microwave signals generation is implemented using a Michelson fiber-optic interferometer with Faraday mirrors. Such interferometer topology provides a doubling of the path length, and reduced gyroscopic effects due to a counter-propagating double pass. Changing the parameters of the generated microwave ultrawideband signals with frequency modulation is achieved by pump current shape and amplitude control. It is also proposed to use real-time oscilloscope without need of changing of the internal structure of such generator to pre-tune it. Time-frequency analysis is used to extract frequency versus time dependence. By so doing, direct impulse response estimation is performed. This method allows to characterize laser diode frequency response for arbitrary microwave waveform generation by means of pump current waveform calculation from experimental data.

Ultrafast modulation of terahertz waves using on-chip dual-layer near-field coupling

As a key potential component of future sixth-generation (6G) communication systems, terahertz (THz) technology has received much attention in recent years. However, a lack of effective high-speed direct modulation of THz waves has limited the development of THz communication technology. Currently, most high-speed modulators are based on photonic systems that can modulate electromagnetic waves with high speed using sophisticated optoelectronic conversion techniques. Yet, they usually suffer from low conversion efficiency of light to the THz range, resulting in low output power of the modulated THz waves. Here, we describe a guided-wave modulator for THz signals whose performance nearly matches that of existing in-line fiber-optic modulators. Our results demonstrate a maximum modulation depth greater than 20 dB (99%) and a maximum sinusoidal modulation speed of more than 30 GHz, with an insertion loss around 7 dB. We demonstrate the capabilities of this modulator in a point-to-point communication link with a 25 Gbit/s modulation speed. Our modulator design, based on near-field coupling of a THz transmission line to a single resonant meta-element, represents a powerful improvement for on-chip integrated high-performance THz devices.

Duty-cycle dependence of photo-induced displacement current in MISIM photocells

Organic optoelectronic conversion possesses various advantages such as low cost and tunable light sensing, but organic semiconductors suffer from significant drawbacks, such as instability in air and low carrier mobility. To overcome them, we recently proposed a [metal (M)|insulator (I)|semiconductor (S)|insulator (I)|metal (M)] structure (MISIM photocells) that can effectively induce photo-induced displacement current without any passage of carriers through the S|I and I|M interfaces. In the present work, we investigated the duty-cycle dependence of MISIM photocells, to determine the guiding principles for improving the speed and efficiency of the optoelectronic conversion toward its practical application. We formed an MISIM photocell consisting of a bilayer of zinc phthalocyanine (ZnPc) and fullerene (C 60 ) as the S layer and parylene C (PC) as the I layers, and tested the dependence of the photocurrent on the duty cycle D = t ON /( t ON + t OFF ), where t ON and t OFF are the light illumination and blocking times, respectively, in one cycle under light modulation. By independently changing t ON and t OFF in the range of 0.2–2.0 μs, the rise time of the transient photocurrent was found to be improved by approximately 30% by the duty cycle. We also revealed that the charge carriers Q generated in one cycle reached their maximum at D ≈ 0.4, and the time average increased gradually with an increase in modulation frequency. This feature of Q was well explained by a theoretical model for the MISIM photocells. • MISIM photocells: Unique optoelectrical conversion suitable for organic materials. • Pure polarization current without any passage of carriers through the S|I and I|M interfaces • Optimization of conversion efficiency and speed by tuning duty cycle. • Enhancement of conversion speed by 30%. • Successful theoretical fit to the photocurrent as a function of the light illumination and blocking times.

Ultrafast Response of Centimeter Scale Thin CsPbBr3 Single Crystal Film Photodetector for Optical Communication.

The photodetector (PD) is the key component to realize efficient optoelectronic conversion signal in the visible light communication (VLC) system. The response speed directly determines the bandwidth of the whole system. Metal halide perovskite is a neotype of low-cost solution processing semiconductor, with strong optical absorption, low trap density, and high carrier mobility, thus has been widely explored in photoelectric detection applications. However, previously reported perovskite polycrystalline photodetectors exhibit limited response speed due to the existence of grain boundaries. Here, an improved confined space method is developed through adjusting the heating area to control nucleation, resulting in centimeter scale fully inorganic perovskite CsPbBr3 thin single crystal films (SCFs) (<40µm). The smooth surface and high crystallinity of CsPbBr3 SCFs render admirable exciton lifetime. The planar metal-semiconductor-metal photodetector using CsPbBr3 SCF as the photosensitive layer demonstrates a limit response time of 200/300ns and a VLC within 100-500kHz frequency for both 365nm and white light, which is superior to previously reported CsPbBr3 polycrystalline filmand single crystal photodetectors.

Wideband Vector Network Analyzer Based on Direct Microwave Photonic Digitization

Vector network analyzers (VNAs) are established as one of the indispensable tools for measuring and analyzing the characteristics of objects under test in various fields, ranging from medicine and material to geology and communication. Conventional VNAs are commonly based on microwave mixing architectures that inevitably compromise accuracy, dynamic range, and bandwidth. Spurred by the deficiencies of conventional VNAs, this paper proposes a wideband photonic vector network analyzer (PVNA) that exploits the concept of direct microwave photonic digitization. In our method, ultra-stable optical trains directly sample the response signals from the objects under test, followed by opto-electronic conversion and quantization, to ultimately obviate the intricate down-conversion procedures in traditional VNAs. The contribution of our method relies on the direct microwave photonic digitization process enabling a novel and compact PVNA architecture that extends the measurable frequency range to 110 GHz with existing commercial devices or even higher by employing a high bandwidth modulator. In any case, our technique reduces the bandwidth requirements of the optical intensity digitizers. To validate our architecture’s theoretical principle, we establish an experimental PVNA with a measurable frequency range of up to 40 GHz and a dynamic range exceeding 90 dB. The developed methodology based on direct microwave photonic digitization paves a new path to the study of broadband, low-cost, and compact VNAs.

Theoretical Investigation of Switch Effect on the Efficiency and Adaptivity of Molecular Optoelectronic Conversion Devices.

Molecular photoswitch can effectively regulate charge separation (CS) and charge recombination (CR) in donor-acceptor (D-A) systems. However, deformation of the donor-switch-acceptor (D-S-A) systems caused by the switch isomerization will destroy the geometrical stability of the battery. Here we take the planar platinum(II) terpyridyl complex of [Pt(t Bu3 tpy)(-C≡C-Ph)n ]+ as the typical D-A model, designed six D-S-A systems using different photoswitches (dimethyldihydropyrene, fulgimide, arylazopyrazole, N-salicylideneaniline, spiropyran, and dithienylethene, denoted as D-S-A 1-6 hereafter). Our investigations show that the D-S-A 1-6 can absorb visible light of 799 nm, 673 nm, 527 nm, 568 nm, 616 nm, and 629 nm, facilitating electrons transfer from the donor and the switch to the acceptor through the Switch-on channel. Then cationic character of the photoswitch can undergo much more rapid isomerization than the neutral form due to the lower energy barrier. The Switch-off isomer breaks the conjugation of the D-S-A system, effectively turning off the CT channel and forming the CS state. Based on the evaluated conjugated backbone twist (CBT) angle, we found that D-S-A 1, 2, 4, 6 exhibit little configurational change and can be good candidates as the organic solar cell. The proposed D-S-A design controlled by the molecular switch may help to develop a solution for solar-harvesting practical applications.

Photoinduced Cross Linkable Polymerization of Flexible Perovskite Solar Cells and Modules by Incorporating Benzyl Acrylate

AbstractFlexible perovskite solar cells possess huge application potential in both outdoor (sunlight) and indoor scenes (artificial low light) owing to their high optoelectronic conversion efficiency and agile integration advantages. In order to further establish their feasibility to meet multi‐scenario applications, here a facile “internal packaging” interface strategy is developed, where a selective light‐cured cross‐linking molecule is leveraged to effectively heal the interface defects over perovskite films. Moreover, the cross‐linked interfacial layer can act as an airtight “protective wall”, preventing the device from water and oxygen corrosion and lead leakage. The flexible devices aided by this strategy show considerable performance ranging from small size to scalable modules (20.86%‐0.07 cm2, 16.75%‐24 cm2). More importantly, the optimal devices yield excellent moisture resistance, light soaking resistance, and lead leakage prevention stability. Based on the common light source environment of indoor scenes, the excellence of flexible modules (30.73% under white light‐emitting diode (LED), 26.48% under yellow LED) is further validated. It is expected that this gentle strategy can underline simultaneous promoting of the efficiency and stability of flexible perovskite modules, thereby accelerating the application of flexible perovskite in advanced industrial fields.