Optoelectronic Functions Research Articles

A Review of Metal-Free Organic Halide Perovskite: Future Directions for the Next Generation of Solar Cells

Herein, a concise survey on the latest enhancements of the recently discovered metal-free halide perovskites (MFHPs) as the last member of the ABX3 perovskite systems is portrayed with regard to its preferential characteristics, functions, and diverse structure. Even with features such as electronic band structures similar to physical characteristics such as liquids applied in optoelectronic systems, the heyday of metal-halide perovskites did not last long, because of the emergence of MFHPs. Indeed, the toxic nature of Pb-containing halide perovskites obstructs scaling up in practice while tending to eco-benign materials utilized in the adjustable design and functional probing has come into view as a significant hotspot in photovoltaic research. The MFHPs emerge with unprecedented properties, including light weight, excellent optoelectronic function, variable chemical structures, adjustability, mechanical adaptability, and environmentally benign procedures. These organic semiconductors with good efficiency and long-term stability are used in light-harvesting devices. Here, in the enterprise to upgrade the latest state of the art, we mean to have a quick browse on the various crystalline structure, synthesis approaches, and different properties of metal-free organic halide materials such as ferroelectric, dielectric, piezoelectric, charge-transport, electrocaloric refrigeration and mechanical properties. Future perspectives on this late-rising category also are submitted.

Controlled Optoelectronic Response in van der Waals Heterostructures for In‐Sensor Computing

AbstractIn‐sensor computing with visual information, which can integrate photo‐sensing, data storage, and computation functions within the same physical element, has promised a fundamentally different architecture for future machine vision technology with extreme energy and time efficiency. The elementary devices required to fulfil the goal of such a new sensory computation scheme would demand a bold functional variation to the existing sensor and data processing hardware. Here, a van der Waals (vdW) heterostructure‐based optoelectronic transistor that can act as an integrated photoreceptor, memory, and computation unit by exploiting its own physical attributes is demonstrated. It is found that diverse photoelectric control of device conductance can lead to versatile photoresponse characteristics, including memristive behaviors, retention‐, polarity‐ and strength‐tunable photoconductance, photoelectric‐coupling effect, etc. Exploiting the photoelectric‐coupling effect, reconfigurable and nonvolatile optoelectronic logic functions are realized in this device, featuring a logic‐in‐sensor unit. With the same device, both short‐ and long‐term synaptic plasticity can be faithfully emulated, rendering it an optoelectronic synaptic transistor. Moreover, a psychologic human memory model is implemented with the device, showing the emulation of memorization and learning processes. This prototypical demonstration provides a promising hardware system for visual information in‐sensor computing capable of addressing complex computation tasks.

Exciton Diffusion and Annihilation in an sp2 Carbon-Conjugated Covalent Organic Framework.

To optimize the optical and optoelectronic functionalities of two-dimensional (2D) covalent organic frameworks (COFs), detailed properties of emissive and nonradiative pathways after photoexcitation need to be elucidated and linked to particular structural designs. Here, we use transient absorption (TA) spectroscopy to study the colloidal suspension of the full sp2 carbon-conjugated sp2c-COF and characterize the spatial extent and diffusion dynamics of the emissive excitons generated by impulsive photoexcitation. The ∼3.5 Å stacking distance between 2D layers results in cofacial pyrene excitons that diffuse through the framework, while the state that dominates the emissive spectrum of the polycrystalline solid is assigned to an extended cofacial exciton whose 2D delocalization is promoted by C═C linkages. The subnanosecond kinetics of a photoinduced absorption (PIA) signal in the near-infrared, attributed to a charge-separated exciton, or polaron pair, reflects three-dimensional (3D) exciton diffusion as well as long-range exciton-exciton annihilation driven by resonance interactions. Within our experimental regime, doubling the excitation intensity results in a 10-fold increase in the estimated exciton diffusion length, from ∼3 to ∼30 nm, suggesting that higher lattice temperature may enhance exciton mobility in the COF colloid.

Two-Dimensional Perovskite-Gated AlGaN/GaN High-Electron-Mobility-Transistor for Neuromorphic Vision Sensor.

The extraordinary optoelectronic properties and continued commercialization of GaN enable it a promising component for neuromorphic visual system (NVS). However, typical GaN‐based optoelectronic devices demonstrated to data only show temporary and unidirectional photoresponse in ultraviolet region, which is an insurmountable obstacle for construction of NVS in practical applications. Herein, an ultrasensitive visual sensor with phototransistor architecture consisting of AlGaN/GaN high‐electron‐mobility‐transistor (HEMT) and two‐dimensional Ruddlesden–Popper organic–inorganic halide perovskite (2D OIHP) is reported. Utilizing the significant variation in activation energy for ion transport in 2D OIHP (from 1.3 eV under dark to 0.4 eV under illumination), the sensor can efficiently perceive and storage optical information in ultraviolet–visible region. Meanwhile, the photo‐enhanced field‐effect mechanism in the depletion‐mode HEMT enables gate‐tunable negative and positive photoresponse, where some typical optoelectronic synaptic functions including inhibitory and excitatory postsynaptic current as well as paired‐pulse facilitation are demonstrated. More importantly, a NVS based on the proposed visual sensor array is constructed for achieving neuromorphic visual preprocessing with an improved color image recognition rate of 100%.

Versatile aza‐BODIPY‐based low‐bandgap conjugated small molecule for light harvesting and near‐infrared photodetection

AbstractThe versatile nature of organic conjugated materials renders their flawless integration into a diverse family of optoelectronic devices with light‐harvesting, photodetection, or light‐emitting capabilities. Classes of materials that offer the possibilities of two or more distinct optoelectronic functions are particularly attractive as they enable smart applications while providing the benefits of the ease of fabrication using low‐cost processes. Here, we develop a novel, multi‐purpose conjugated small molecule by combining boron‐azadipyrromethene (aza‐BODIPY) as electron acceptor with triphenylamine (TPA) as end‐capping donor units. The implemented donor–acceptor–donor (D–A–D) configuration, in the form of TPA‐azaBODIPY‐TPA, preserves ideal charge transfer characteristics with appropriate excitation energy levels, with the additional ability to be used as either a charge transporting interlayer or light‐sensing semiconducting layer in optoelectronic devices. To demonstrate its versatility, we first show that TPA‐azaBODIPY‐TPA can act as an excellent hole transport layer in methylammonium lead triiodide (MAPbI3)‐based perovskite solar cells with measured power conversion efficiencies exceeding 17%, outperforming control solar cells with PEDOT:PSS by nearly 60%. Furthermore, the optical bandgap of 1.49 eV is shown to provide significant photodetection in the wavelength range of up to 800 nm where TPA‐azaBODIPY‐TPA functions as donor in near‐infrared organic photodetectors (OPDs) composed of fullerene derivatives. Overall, the established versatility of TPA‐azaBODIPY‐TPA, combined with its robust thermal stability as well as excellent solubility and processability, provides a new guide for developing highly efficient multi‐purpose electronic materials for the next‐generation of smart optoelectronic devices.image

Single‐Photon Emission from Single Microplate MAPbI3 Nanocrystals with Ultranarrow Photoluminescence Linewidths and Exciton Fine Structures

AbstractStimulated by the superior performance of organic–inorganic MAPbI3 perovskite films in photovoltaic devices, a lot of research interest is now being devoted to their low‐dimensional nanocrystals (NCs) to extend the optoelectronic functionalities as well as to promote the potential applications in quantum information technologies. Compared to other organic–inorganic and all‐inorganic counterparts that have been intensively studied, the MAPbI3 NCs suffer from the optical and chemical instabilities so that their single‐particle photophysical properties have been largely unexplored up to now. Here, the authors have synthesized single MAPbI3 microplates from a two‐step method and characterize their optical properties mainly at the cryogenic temperature, showing that localized optical emitters are universally present with the quantum feature of single‐photon emission. Photoluminescence (PL) linewidth measured for such a single quantum emitter can be as narrow as ≈200 μeV, as a direct consequence of its embedment inside the microplate with the spectral diffusion effect being greatly suppressed. This has allowed them to resolve the exciton fine structures from some of the studied single quantum emitters, each of which is manifested as a PL doublet with the energy separation of ≈600 μeV and the orthogonally linear polarizations.

Horizontally Self-Standing Growth of Bi2 O2 Se Achieving Optimal Optoelectric Properties.

Air-stable 2D Bi2 O2 Se material with high carrier mobility appears as a promising semiconductor platform for future micro/nanoelectronics and optoelectronics. Like most 2D materials, Bi2 O2 Se 2D nanostructures normally form on atomically flat mica substrates, in which undesirable defects and structural damage from the subsequent transfer process will largely degrade their photoelectronic performance. Here, a new synthesis route involving successive kinetic and thermodynamic processes is proposed to achieve horizontally self-standing Bi2 O2 Se nanostructures on SiO2 /Si substrates. Fewer defects and avoidance of transfer procedure involving corrosive solvents ensure the integrity of the intrinsic lattice and band structures in Bi2 O2 Se nanostructures. In contrast to flat structures grown on mica, it displays reduced dark current and improved photoresponse performance (on-off ratio, photoresponsivity, response time, and detectivity). These results indicate a new potential in high-quality 2D electronic nanostructures with optimal optoelectronic functionality.

High-performance non-fullerene acceptor inverted organic photovoltaics incorporating solution processed doped metal oxide hole selective contact

Inverted organic photovoltaics (OPVs) allow flexibility on designing a roll-to-roll production process of OPVs, providing technological opportunities. The OPV roll-to-roll production process demands thick and high-performance solution-based hole selective contacts. Here, we show that a solution processed antimony-doped tin oxide (ATO) hole selective contact produced by spray pyrolysis route exhibits exceptional optoelectronic properties and functionality within non-fullerene acceptor PM6:Y6:PC70BM inverted OPVs. The corresponding solution processed inverted OPVs provide high power conversion efficiency values when a thick hole selective contact of solution processed doped ATO is incorporated within the inverted OPV device structure and similar light stability to that achieved with the commonly used thermally evaporated MoO3 hole selective contact.

On an oxadiazole-pyridine derived diimine ligand and its Re complex: Synthesis, characterization and photophysical features

Recent development of optoelectronic functional films, photovoltaic devices, photocatalysts and display devices has attracted widespread attention on the design and synthesis of emitters and dyes with optoelectronic functions. Among these proposed emitters and dyes, polypyridine Re(I) carbonyl complexes are unique ones due to their simple molecular structure, which makes their chemical modification easy to perform. These Re(I) complexes could be explored as singlet oxygen (1O2) photosensitizer, which broadens their application. In this work, an electron-accepting diimine ligand with -CF3 group was incorporated into a Re(I) complex (denoted as Re-LCF3). This Re(I) complex was characterized by single crystal analysis, electronic structure analysis, photophysical property analysis, so that its phosphorescent nature was confirmed. Then Re-LCF3 was dispersed into nanofibers of polyvinylpyrrolidone by means of electro-spinning method, hoping to improve 1O2-producing performance of the resulting composite nanofibers (denoted as Re-LCF3@PVP). A full comparison between Re-LCF3 in solid state, in solution, in polymer fibers was performed, including their absorption, emission, quantum yield, lifetime and 1O2-producing performance. It was found that the photophysical performance of Re-LCF3@PVP was better than that of pure Re-LCF3 in solid state, showing emission blue shift, improved photostability, longer lifetime and better emission quantum yield. The 1O2-producing performance of Re-LCF3@PVP was better than that of pure Re-LCF3 in solid state.

Photonic and optoelectronic neuromorphic computing

Recent advances in neuromorphic computing have established a computational framework that removes the processor-memory bottleneck evident in traditional von Neumann computing. Moreover, contemporary photonic circuits have addressed the limitations of electrical computational platforms to offer energy-efficient and parallel interconnects independently of the distance. When employed as synaptic interconnects with reconfigurable photonic elements, they can offer an analog platform capable of arbitrary linear matrix operations, including multiply–accumulate operation and convolution at extremely high speed and energy efficiency. Both all-optical and optoelectronic nonlinear transfer functions have been investigated for realizing neurons with photonic signals. A number of research efforts have reported orders of magnitude improvements estimated for computational throughput and energy efficiency. Compared to biological neural systems, achieving high scalability and density is challenging for such photonic neuromorphic systems. Recently developed tensor-train-decomposition methods and three-dimensional photonic integration technologies can potentially address both algorithmic and architectural scalability. This tutorial covers architectures, technologies, learning algorithms, and benchmarking for photonic and optoelectronic neuromorphic computers.

Visualization of Band Shifting and Interlayer Coupling in WxMo1–xS2 Alloys Using Near-Field Broadband Absorption Microscopy

Beyond-diffraction-limit optical absorption spectroscopy provides in-depth information on the graded band structures of composition-spread and stacked two-dimensional materials, in which direct/indirect bandgap, interlayer coupling, and defects significantly modify their optoelectronic functionalities such as photoluminescence efficiency. We here visualize the spatially varying band structure of monolayer and bilayer transition metal dichalcogenide alloys by using near-field broadband absorption microscopy. The near-field spectral and spatial information manifests the excitonic band shift that results from the interplay of composition spreading and interlayer coupling. These results enable us to identify, notably, the top layer of the bilayer alloy as pure WS2. We also use the aberration-free near-field transmission images to demarcate the exact boundaries of alloyed and pure transition metal dichalcogenides. This technology can offer valuable insights on various layered structures in the era of "stacking science" in the quest of quantum optoelectronic devices.

Electrically Tunable Second Harmonic Generation in Atomically Thin ReS2.

Electrical tuning of second-order nonlinearity in optical materials is attractive to strengthen and expand the functionalities of nonlinear optical technologies, though its implementation remains elusive. Here, we report the electrically tunable second-order nonlinearity in atomically thin ReS2 flakes benefiting from their distorted 1T crystal structure and interlayer charge transfer. Enabled by the efficient electrostatic control of the few-atomic-layer ReS2, we show that second harmonic generation (SHG) can be induced in odd-number-layered ReS2 flakes which are centrosymmetric and thus without intrinsic SHG. Moreover, the SHG can be precisely modulated by the electric field, reversibly switching from almost zero to an amplitude more than 1 order of magnitude stronger than that of the monolayer MoS2. For the even-number-layered ReS2 flakes with the intrinsic SHG, the external electric field could be leveraged to enhance the SHG. We further perform the first-principles calculations which suggest that the modification of in-plane second-order hyperpolarizability by the redistributed interlayer-transferring charges in the distorted 1T crystal structure underlies the electrically tunable SHG in ReS2. With its active SHG tunability while using the facile electrostatic control, our work may further expand the nonlinear optoelectronic functions of two-dimensional materials for developing electrically controllable nonlinear optoelectronic devices.

Thin-film lithium-niobate electro-optic platform for spectrally tailored dual-comb spectroscopy

Laser frequency comb generators on photonic chips open up the exciting prospect of integrated dual-comb microspectrometers. Amongst all nanophotonic platforms, the technology of low-loss thin-film lithium-niobate-on-insulator shows distinguishing features, such as the possibility to combine various optoelectronic and nonlinear optical functionalities that harness second- and third-order nonlinearities, and thus promises the fabrication of a fully on-chip instrument. Here, a critical step towards such achievement is demonstrated with an electro-optic microring-based dual-comb interferometer. Spectra centered at 191.5 THz and spanning 1.6 THz (53 cm−1) at a resolution of 10 GHz (0.33 cm−1) are obtained in a single measurement without requiring frequency scanning or moving parts. The frequency agility of the system enables spectrally-tailored multiplexed sensing, which allows for interrogation of non-adjacent spectral regions, here separated by 6.6 THz (220 cm−1), without compromising the signal-to-noise ratio. Our studies show that electro-optic-based nanophotonic technology holds much promise for new strategies of molecular sensing over broad spectral bandwidths.

Integrated photoelectrochromic supercapacitor for applications in energy storage and smart windows

While electrochromic devices have been proposed and developed specially for multifunctional smart windows, they still need to be charged by an external power source, which increases complicated installation costs and energy consumption. In spite of efforts dedicated to develop monomer device that combines electrochromic and optoelectronic functions to address aforementioned issue, the practical application is still limited by complication in device structure, expensive cost, and unsatisfied device performance. The current work provides a facile and feasible strategy to fabricate the monomer photovoltaic electrochromic supercapacitors device by integrating dye-sensitized solar cells (DSSC) and electrochromic supercapacitors (ESC) based on the WS2-WO3 counter electrode of DSSC and WO3 electrodes of ESC. As a proof-of-concept presented here, in a typical single device, the ESC achieved an area specific capacitance of 69.9 mF cm−2 and 91.89% capacitance retention after 2000 cycles. In addition, the device exhibited a fast coloring/discoloring response in 30 s. The multifunctional smart window not only can be used as typical electrochromic window, but also can be used as energy storage device simultaneously, providing promise for a wide range of applications in buildings, airplanes, automobiles, etc.

A GGA + vdW study on electronic properties and optoelectronic functionality of Cd-doped tetragonal CH3NH3PbI3 for photovoltaics

The electronic properties and optoelectronic functionalities of tetragonal CH 3 NH 3 PbI 3 doped with different concentrations (6.25%, 12.5% and 25%) of Cd have been investigated using the the generalized gradient approximation with the correction of van der Waals interactions (GGA + vdW). First, we examine the dependence of band gap on the Cd doping concentration, and find that the increased Cd content narrows the band gap up to 1.41 eV, extending the photoabsorption wavelength of CH 3 NH 3 PbI 3 into the range of near-infrared spectrum. Furthermore, the electron mobility is found to be enhanced by 28%, which is beneficial for separating and collecting the photo-excited carriers. The effects of band-gap reduction and electron-mobility enhancement jointly contribute to the promotion in optoelectronics of CH 3 NH 3 PbI 3 . The detailed analyses on the thermodynamic stabilities of doped structures have been made through examining their phonon dispersions and decomposition energies. This work has implications in offering guidance for broadening the photovoltaic applications of CH 3 NH 3 PbI 3 .

Thermal Camouflaging MXene Robotic Skin with Bio‐Inspired Stimulus Sensation and Wireless Communication

AbstractCephalopod skin, which is capable of dynamic optical camouflage, environmental perceptions, and herd communication, has long been a source of bio‐inspiration for developing soft robots with incredible optoelectronic functions. Yet, challenges still exist in designing a stretchable and compliant robotic skin with high‐level functional integration for soft robots with infinite degrees of freedom. Herein, an emerging 2D material, Ti3C2Tx MXene, and an interfacial engineering strategy are adopted to fabricate the soft robotic skin with cephalopod skin‐inspired multifunctionality. By harnessing interfacial instability, the MXene robotic skin with reconfigurable microtextures demonstrates tunable infrared emission (0.30–0.80), enabling dynamic thermal camouflage for soft robots. Benefiting from the intrinsic Seebeck effect, crack propagation behaviors as well as high electrical conductivity, the MXene robotic skins are tightly integrated with thermal/strain sensation capabilities and can serve as a deformable antenna for wireless communication. Without additional electronics installed, the soft robots wearing the conformal MXene skins perform adaptive thermal camouflage based on the thermoelectric feedback in response to environmental temperature changes. With built‐in strain sensing and wireless communication capabilities, the soft robot can record its locomotion routes and wirelessly transmit the key information to the following soft robot to keep both in disguise under thermographic cameras.

Optical Arbitrary Waveform Measurement (OAWM) Using Silicon Photonic Slicing Filters

We demonstrate an optical arbitrary waveform measurement (OAWM) system that exploits a bank of silicon photonic (SiP) frequency-tunable coupled-resonator optical waveguide (CROW) filters for gapless spectral slicing of broadband optical signals. The spectral slices are coherently detected using a frequency comb as a multi-wavelength local oscillator (LO) and stitched together by digital signal processing (DSP). For high-quality signal reconstruction, we have implemented a maximum-ratio combining (MRC) technique based on precise calibration of the complex-valued opto-electronic transfer functions of all detection paths. In a proof-of-concept experiment, we demonstrate the viability of the scheme by implementing a four-channel system that offers an overall detection bandwidth of 140 GHz. Exploiting a femtosecond laser with precisely known pulse shape for calibration along with dynamic amplitude and phase estimation, we reconstruct 100 GBd QPSK, 16QAM and 64QAM optical data signals. The reconstructed signals show improved quality compared to that obtained with a single high-speed intradyne receiver, while the electronic bandwidth requirements of the individual coherent receivers are greatly reduced.

Structure and properties of Er and Er/Yb-doped YF3 up-conversion phosphors compared with oxide hosts through an internal standard

YF3 has useful physico-chemical properties such as low refractive index, low phonon energies, large infrared (IR) transparency and wide band gap, making it one of the most interesting materials with optical and optoelectronic functionalities. Among different applications, YF3 appears very promising as a host matrix for lanthanide (Ln) ion doping, in particular for up-conversion photoluminescence (UCPL). In the present study, YF3 has been synthesized via a fluorolytic sol-gel (SG) route leading to a precursor solution of yttrium trifluoroacetate (Y-TFA), from which YF3 and other oxidized derivatives can be obtained by thermal decomposition. The influence of temperature on the phases obtained was investigated by Differential Scanning Calorimetry (DSC), together with an in-depth study of the crystallite sizes by Scanning Electron Microscopy (SEM) and X-ray diffraction (XRD). Representative NIR to visible UCPL spectra excited at 980 nm are presented for Er and Er/Yb-doped YF3 and the corresponding UC mechanisms are discussed based on 980 nm laser power dependence plots. Moreover, an internal standard method is utilized to compare YF3 with other selected oxide matrices for lanthanides, namely aluminosilicate glass (90 SiO2-10 AlO1.5), titania (TiO2) and yttria (Y2O3).

Emerging New‐Generation Detecting and Sensing of Metal Halide Perovskites

AbstractThe unique energy conversion characteristics of metal halide perovskite (MHP) materials, which can be hardly observed in conventional semiconductors and metal oxides, have boosted their promising application in detecting and sensing devices, in addition to their famous optoelectronic functions. Herein, the recent progresses of the state‐of‐the‐art applications of MHPs are focused on X‐ray diagnosis, cardiac detection, bionic retina, artificial synapse, cell imaging, and others. Owing to their emerging electrical properties with multifield coupled response effect, and photoelectric, electro‐optical, and all‐optical conversion functions, MHPs demonstrate promising prospects in the diagnosis and treatment of various diseases. As functional optoelectronic materials, MHPs provide a new platform for future biomedical devices. This review article is expected to present the current status on, and further promote the application of MHP materials in detecting and sensing devices.

A High-Performance In-Memory Photodetector Realized by Charge Storage in a van der Waals MISFET.

The emerging data-intensive applications in optoelectronics are driving innovation toward the fused integration of sensing, memory, and computing to break through the restrictions of the von Neumann architecture. However, the present photodetectors with only optoelectronic conversion functions cannot satisfy the growing demands of the multifunctions required in single devices. Here, a novel route for the integration of non-volatile memory into a photodetector is proposed, with a WSe2 /h-BN van der Waals heterostructure on a Si/SiO2 substrate to realize in-memory photodetection. This photodetector exhibits an ultrahigh readout photocurrent of 3.4 µA and photoresponsivity of 337.8 A W-1 in the solar-blind wavelength region, together with an extended retention time of more than 10 years. Furthermore, the charge-storage-based non-volatile mechanism of h-BN/SiO2 is successfully proven through a novel analysis of in situ optoelectronic electron energy-loss spectroscopy. These results represent a leap forward to future applications and insightful mechanisms of in-memory photodetection.