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The accelerated photoresponse of OPD devices for axial fluorinated SubPc was confirmed by photovoltaic analysis and theoretical simulations.

A novel series of donor (D)-π-acceptor (A) merocyanine molecules harnessed with intramolecular chalcogen bonding (ChaB) is designed, synthesized, and characterized. ChaB comprises periodic chalcogen atoms, S, Se, and Te, and a neighboring oxygen atom of a carbonyl moiety. Compared to the D-π-A merocyanine dye with nontraditional intramolecular hydrogen bonding, the novel molecules with an intramolecular ChaB exhibit remarkably smaller absorption spectral widths and higher absorption coefficients attributed to their cyanine-like characteristics approaching the resonance parameter (

Electronic devices composed of semiconducting two-dimensional (2D) materials and ultrathin 2D metallic electrode materials, accompanying synergistic interactions and extraordinary properties, are becoming highly promising for future flexible and transparent electronic and optoelectronic device applications. Unlike devices with bulk metal electrode and 2D channel materials, devices with ultrathin 2D electrode and 2D channel are susceptible to chemical reactions in both channel and electrode surface due to the high surface to volume ratio of the 2D structures. However, so far, the effect of doping was primary concerned on the channel component, and there is lack of understanding in terms of how to modulate electrical properties of devices by engineering electrical properties of both the metallic electrode and the semiconducting channel. Here, we propose the novel, one-pot doping of the field-effect transistor (FET) based on 2D molybdenum disulfide (MoS

Stacked structures employing wavelength-selective organic photodiodes (OPDs) have been studied as promising alternatives to the conventional Si-based image sensors because of their color constancy. Herein, novel donor (D)-π-acceptor (A) molecules are designed, synthesized, and characterized as green-light-selective absorbers for application in organic-on-Si hybrid complementary metal-oxide-semiconductor (CMOS) color image sensors. The p-type molecules, combined with two fused-type heterocyclic donors and an electron-accepting unit, exhibit cyanine-like properties that are characterized by intense and sharp absorption. This molecular design leads to improved absorption properties, thermal stability, and higher photoelectric conversion compared to those of a molecular design based on a nonfused ring. A maximum external quantum efficiency of 66% (λ

The present work describes the development of an organic photodiode (OPD) receiver for high-speed optical wireless communication. To determine the optimal communication design, two different types of photoelectric conversion layers, bulk heterojunction (BHJ) and planar heterojunction (PHJ), are compared. The BHJ-OPD device has a -3 dB bandwidth of 0.65 MHz (at zero bias) and a maximum of 1.4 MHz (at -4 V bias). A 150 Mbps single-channel visible light communication (VLC) data rate using this device by combining preequalization and machine learning (ML)-based digital signal processing (DSP) is demonstrated. To the best of the authors' knowledge, this is the highest data rate ever achieved on an OPD-based VLC system by a factor of 40 over the previous fastest reported. Additionally, the proposed OPD receiver achieves orders of magnitude higher spectral efficiency than the previously reported organic photovoltaic (OPV)-based receivers.

The demand for high-definition complementary metal-oxide–semiconductor (CMOS) image sensors has increased considerably over the past few years in industry as well as in academia. Here we propose transparent green-sensitive organic photodetectors (TG-OPDs) with both dark-current-based high detectivity (over 10 14 c m H z 1 / 2 W − 1 at a wavelength of 550 nm under 3 V) and high responsivity ( 0.34 A W − 1 under 3 V) for organic–silicon hybrid CMOS image sensors. A b a t h o c u p r o i n e : C 60 electron-transporting layer provided the fabricated TG-OPDs with a minimal junction resistivity, smooth morphology, and desirable energy level modulation, resulting in exceptional light sensitivity, a low dark current (below 10 − 11 A c m − 2 ), and a high rectification ratio spanning 10 orders of magnitude. The TG-OPDs had high-temperature endurance (up to 150°C for 2 h) and operational stability under intense heat (above 85°C) for 50 d. We expect this performance to enable the industrialization of these TG-OPDs for optoelectronic sensor applications, such as photoplethysmography, fingerprint recognition, proximity sensing, and imaging.

A bulk-heterojunction (BHJ) structure of organic semiconductor blend is widely used in photon-to-electron converting devices such as organic photodetectors (OPD) and photovoltaics (OPV). However, the impact of the molecular structure on the interfacial electronic states and optoelectronic properties of the constituent organic semiconductors is still unclear, limiting further development of these devices for commercialization. Herein, the critical role of donor molecular structure on OPD performance is identified in highly intermixed BHJ blends containing a small-molecule donor and C60 acceptor. Blending introduces a twisted structure in the donor molecule and a strong coupling between donor and acceptor molecules. This results in ultrafast exciton separation (

As organic photodetectors with less than 1 μm pixel size are in demand, a new way of enhancing the sensitivity of the photodetectors is required to compensate for its degradation due to the reduction in pixel size. Here, we used Ag nanoparticles coated with SiOxNy as a light-absorbing layer to realize the scale-down of the pixel size without the loss of sensitivity. The surface plasmon resonance appeared at the interface between Ag nanoparticles and SiOxNy. The plasmon resonance endowed the organic photodetector with boosted photon absorption and external quantum efficiency. As the Ag nanoparticles with SiOxNy are easily deposited on ITO/SiO2, it can be adapted into various organic color image sensors. The plasmon-supported organic photodetector is a promising solution for realizing color image sensors with high resolution below 1 μm.

Utilizing organic electronics compatible with conventional semiconductor fabrication processes is extremely difficult because of their low chemical resistivity and poor environmental durability. To preserve the intrinsic functionality of organic materials, only a few fabrication processes can be used. Moreover, it is essential to achieve process expandability and silicon-process compatibility to develop high-resolution electronics suitable for mass production. Therefore, we developed wet-process-compatible organic photodetectors by replacing the conventional shadow-mask process with photolithography. This suppresses particle deposition during the serial fabrication processes, providing high operational stability. The fabricated green organic photodiodes exhibit a low dark current (1.0 × 10−11 A/cm2) with high photon–electron conversion efficiency (EQE = 65%). The charge collection and charge separation efficiencies are stable (ηcc = 84.6% and ηcs = 97.7%, respectively). Moreover, the organic semiconductors are compatible with conventional wet- and dry-etching processes owing to thin-film encapsulation layers. Finally, the novel organic image sensor can withstand 500 h under 85 °C/85% relative humidity and 1000 thermal cycles (−55–125 °C). Because of its robustness and strong barrier properties, the novel process architecture reported herein can be extended to any organic electronic devices, including widely commercialized organic light-emitting diodes and organic photovoltaic devices.

A novel approach for the thin film encapsulation (TFE) of organic photo-diode (OPD) for the next generation of organic/inorganic hybrid complementary metal oxide semiconductor (CMOS) image sensor is reported. The TFE is composed of two different metal-oxides stacked in bi-layer thin film architecture. The first layer is composed of aluminum oxide (AlOx) deposited by atomic layer deposition (ALD) at a moderate temperature of 100 °C to avoid any damage to the organic active layer. The first layer acts as a water barrier layer and also as a first protective layer for the deposition of a second silicon oxynitride (SiON) layer that could be processed by plasma-enhanced chemical vapor deposition (PECVD) at higher temperatures. The second layer ensures a better mechanical and chemical stability of the whole structure and also serves as a second protective layer from damages induced during the additional processing stages, such as photolithography or microlensing. With the TFE architecture the overall device stability at 85 °C and 85% relative humidity exceeded 1000 h without observable device performance decrease. This was confirmed by fabricating a green-light sensitive OPD characterized by a stable external quantum efficiency of 60–70%.

In this work, organic photodiodes (OPDs) based on two newly synthesized p-type dipolar small molecules are reported for application to green-light-selective OPDs. In order to reduce the blue-color absorption induced by the use of C60 as the n-type material in a bulk heterojunction (BHJ), the electron donor:electron acceptor composition ratio is tuned in the BHJ. With this light manipulation approach, the blue-wavelength external quantum efficiency (EQE) is minimized to 18% after reducing the C60 concentration in the center part of the BHJ. The two p-type molecules get a cyanine-like character with intense and sharp absorption in the green color by adjusting the strength of their donating and accepting parts and by choosing a selenophene unit as a π-linker. When combined to C60, the green-wavelength EQE reaches 70% in a complete device composed of two transparent electrodes. Finally, the optical simulation shows the good color-balance performance of hybrid full-color image sensor without an additional filter by using the developed green OPD as the top-layer in stacked device architecture.

We report on two novel p-type small molecules with a donor–acceptor molecular structure for application to green-light-selective organic photodiodes (OPDs). To achieve the requirement of high light selectivity and sensitivity, an electron-donating aryl amino moiety is combined with two respective electron-accepting heterocycles so that the molecules approach cyanine-like character, characterized by intense and sharp absorption. Molecular stacking is controlled by the addition of bulky aryl functional groups to the main backbone to further control the electrical charge transport properties. With this molecular design, a maximum external quantum efficiency close to 61% (λmax = 550 nm) and a dark-current density below 1.6 nA cm−2 (or specific detectivity D* = 1.19 × 1013 cm Hz1/2 W−1) at an applied reverse bias of 3 V are obtained when mixed with fullerene (C60) in an inverted-structure bulk heterojunction OPD composed of two transparent electrodes. The potential construction of a full-color photodetector or an image sensor is demonstrated by combining the green-light-selective OPD with a silicon photodiode containing solely blue and red color filters in a stacked architecture.

As organic photodetectors with less than 1 μm pixel size are in demand, a new way of enhancing the sensitivity of the photodetectors is required to compensate for its degradation due to the reduction in pixel size. Here, we used Ag nanoparticles coated with SiO

Controlling defect states in a buffer layer for organic photo devices is one of the vital factors which have great influence on the device performance. Defect states in silicon oxynitride (SiOxNy) buffer layer for organic photo devices can be controlled by introducing appropriate dopant materials. We performed ab initio simulations to identify the effect on doping SiOxNy with carbon (C), boron (B), and phosphorous (P) atoms. The results unveil that hole defects in the SiOxNy layer diminish with the phosphorous doping. Based on the simulation results, we fabricate the small molecule organic photodetector (OPD) including the phosphorous-doped SiOxNy buffer layer and the active film of blended naphthalene-based donor and C60 acceptor molecules, which shows excellent enhancement in the external quantum efficiency (EQE). The results of our charge-based deep level transient spectroscopy (Q-DLTS) measurements confirmed that the EQE enhancement originates from the decrease of the hole traps induced by the reduced hole defects. The method of controlling the defect states in SiOxNy buffer layers by the doping can be used to improve the performance in various organic photo devices.

tuning in the whole visible regime through large changes in the particle-particle separation originating from the electrophoretic movement of the charged particles while maintaining the ordered crystal structure under the external fields.[10] In spite of these merits, there is no report that considered these systems applicable for reversible switching for practical application. Although de-ionized water is the most suitable dispersion medium for producing high quality periodic crystalline structures with enhanced reflectance in these systems, the electrolysis of water molecules at the indium tin oxide (ITO) surface produces significant amounts of H+ and OH− ions as by-products at the cathode and anode, respectively. Therefore, the diffusion of those ions into colloidal arrays substantially limits the tuning stability and range because this phenomena induces decreased thickness of electrical double layer on the surface of the colloidal nanoparticles. To solve this problem, ITO surface was modified by various dielectric insulator passivation layers, including SiO2, SiN, polyimide, and parylene that can block electrochemical reactions at the electrodes (unpublished results). However, this methodology resulted in a substantial reduction of the color tuning range due to decreases in voltage applied to the colloidal dispersion because of the large amount of additional impedance introduced by the passivation layer. Considering the volume resistivity of these commonly used passivation materials (∼1016 Ω m), required thickness of the passivation layer should be at the sub-nm scale in order not to decrease the voltage applied significantly in colloidal dispersion. Preparation of such a thin and uniform film without any defected area is extremely difficult to achieve. Here we report our effort for achieving enhanced tuning stability of the colloidal photonic crystal composed of long-range ordered crystalline colloidal arrays through modifying the ITO electrode with ion exchange resins. The thin layer of over-coating on the ITO surface allowed increased number of cycles of stable color-tuning switching from red to green over 800 times, which is the best result ever reported for a tunable photo nic crystal whose Δλ can be manipulated more than 100 nm. Figure 1(a) depicts the device structure of a unit pixel and the concept of improving the stability of photonic structural color tuning through blocking ion diffusion from both electrodes by coating the electrode surface with a layer of ion-exchange resin. A colloidal dispersion composed of monodisperse 138 nm-diameter polystyrene (PS) nanoparticles dispersed in deionized water was injected between two electrodes. The strong negative charge of the nanoparticles and their thick electrical double layer induce the self-assembly of the long-range ordered colloids through electrostatic repulsion, which dominates the Structural Color Manipulation Using Tunable Photonic Crystals with Enhanced Switching Reliability

Active tunable plasmonic cap arrays were fabricated on a flexible stretchable substrate using a combination of colloidal lithography, lift-up soft lithography, and subsequent electrostatic assembly of gold nanoparticles. The arrangement of the plasmonic caps could be tuned under external strain to deform the substrate in reversible. Real-time variation in the arrangement could be used to tune the optical properties and the electromagnetic field enhancement, thereby a proving a promising mechanism for optimizing the SERS sensitivity.

An electrically tunable photonic crystal is developed utilizing crystalline colloidal arrays of high refractive index particles. Through modulation of the refractive index of the particle, and the applied electric field, both the bandwidth and position of the photonic bandgap could be tuned. Full color modulation with high optical quality is achieved, which paves a way to develop a novel reflective display.

There are growing opportunities and demands for image sensors that produce higher-resolution images, even in low-light conditions. Increasing the light input areas through 3D architecture within the same pixel size can be an effective solution to address this issue. Organic photodiodes (OPDs) that possess wavelength selectivity can allow for advancements in this regard. Here, we report on novel push–pull D−π–A dyes specially designed for Gaussian-shaped, narrow-band absorption and the high photoelectric conversion. These p-type organic dyes work both as a color filter and as a source of photocurrents with linear and fast light responses, high sensitivity, and excellent stability, when combined with C60 to form bulk heterojunctions (BHJs). The effectiveness of the OPD composed of the active color filter was demonstrated by obtaining a full-color image using a camera that contained an organic/Si hybrid complementary metal-oxide-semiconductor (CMOS) color image sensor.

Thin-film color reflectors inspired by Morpho butterflies are fabricated. Using a combination of directional deposition, silica microspheres with a wide size distribution, and a PDMS (polydimethylsiloxane) encasing, a large, flexible reflector is created that actually provides better angle-independent color characteristics than Morpho butterflies and which can even be bent and folded freely without losing its Morpho-mimetic photonic properties.

Recent advances in nanofabrication techniques have enabled the creation of various metallic nanostructures in order to engineer the location and properties of electromagnetic hot spots in a controlled manner. However, most previous methods usually require complicated and time-consuming techniques, and the integration of metallic nanostructures into simple, low-cost devices for chemical or biological sensing is still challenging. Here, we report a promising new strategy for the fabrication of large-area gold nanowell arrays with novel geometric features that makes use of the trapping of self-assembled colloidal particles on a polymer surface. Through both systematic experimental and theoretical analysis, we confirm that the strong plasmon resonances of the proposed nanowell structures are associated with localized surface plasmon resonance (LSPR) on the brims of the nanoholes in the top gold films as well as in the bottom gold disks. In addition, we demonstrate a novel optofluidic platform with built-in subwavelength nanowell arrays that exhibits strong plasmon resonances within microfluidic chips. In our optofluidic systems, the plasmon coupling between the brims and the disks of nanowells makes the plasmon resonance more sensitive to surrounding materials. The dependence of the plasmon resonance on the refractive index of the surrounding medium is found to be as high as 570 nm RIU(-1) (refractive index units). These data lead to a figure of merit (FOM), the slope of refractive index sensitivity in eV RIU(-1)/line width (eV), as high as 4.1.

This work was supported a grant from the Creative Research Initiative Program of the Ministry of Science and Technology for ‘‘Complementary Hybridization of Optical and Fluidic Devices for Integrated Optofluidic Systems.’’ The authors also appreciated partial support from the Brain Korea 21 Program. Supporting Information is available online from Wiley InterScience or from the author.

The spontaneous crystallization of colloidal particlesprovides a simple and cheap alternative to nanolithographyfor creating three-dimensional periodic structures. Colloidalcrystals with long-range order diffract light and displayphotonic bandgaps, which is of practical significance forphotonic and phononic crystal devices

We prepared polymeric structures with unusual complexity in surface morphology derived from photocurable emulsion droplets dispersed in an aqueous medium. The emulsion droplets a few tens of micrometers in size were stabilized with relatively small hydrophobic particles that were bound to the emulsion interfaces. The particle binding tended to immobilize the oil-in-water emulsion interface and dramatically increased the structural relaxation time of the interface deformation over a few days relative to a few milliseconds for an otherwise clean interface. In particular, perfectly immobilized emulsion drops maintained nonspherical elongated structures that were formed by shear-induced emulsification and could not be relaxed to a spherical shape. This property is useful for broad research areas ranging from crystallography and buckling phenomena to materials fabrication. The configuration of small particles on the interface and the “raspberry” shape of particle-stabilized emulsions were captured successfully...

Complementary metal–oxide–semiconductor (CMOS) colour image sensors are representative examples of light-detection devices. To achieve extremely high resolutions, the pixel sizes of the CMOS image sensors must be reduced to less than a micron, which in turn significantly limits the number of photons that can be captured by each pixel using silicon (Si)-based technology (i.e., this reduction in pixel size results in a loss of sensitivity). Here, we demonstrate a novel and efficient method of increasing the sensitivity and resolution of the CMOS image sensors by superposing an organic photodiode (OPD) onto a CMOS circuit with Si photodiodes, which consequently doubles the light-input surface area of each pixel. To realise this concept, we developed organic semiconductor materials with absorption properties selective to green light and successfully fabricated highly efficient green-light-sensitive OPDs without colour filters. We found that such a top light-receiving OPD, which is selective to specific green wavelengths, demonstrates great potential when combined with a newly designed Si-based CMOS circuit containing only blue and red colour filters. To demonstrate the effectiveness of this state-of-the-art hybrid colour image sensor, we acquired a real full-colour image using a camera that contained the organic-on-Si hybrid CMOS colour image sensor.

Electrospun nanofibers were used as confining geometries for fabricating 1-D colloidal assemblies. Silica particles dispersed in several different polymer solutions were cast into nanofibers by an electrospinning process. The silica particle configurations were examined in terms of the size ratio of silica particles to nanofibers and the properties of the dispersing medium. As the electrospun fiber was extended highly, the silica particles dispersed in the polymer solution began to assemble spontaneously into a pearl-necklace structure. We also demonstrated the alignment of 1-D silica assemblies using a designed configuration of collector electrodes.

One-dimensional smart probes based on nanowires and nanotubes that can safely penetrate the plasma membrane and enter biological cells are potentially useful in high-resolution and high-throughput gene and drug delivery, biosensing and single-cell electrophysiology. However, using such probes for optical communication across the cellular membrane at the subwavelength level remains limited. Here, we show that a nanowire waveguide attached to the tapered tip of an optical fibre can guide visible light into intracellular compartments of a living mammalian cell, and can also detect optical signals from subcellular regions with high spatial resolution. Furthermore, we show that through light-activated mechanisms the endoscope can deliver payloads into cells with spatial and temporal specificity. Moreover, insertion of the endoscope into cells and illumination of the guided laser did not induce any significant toxicity in the cells.

Superhydrophobic nanofiber films were created from electrospun nanofibers with undulated surfaces at multiple scales in micrometers and nanometers. The electrospun nanofibers were produced out of aqueous solutions which contained water-soluble polymers and different colloids: monodisperse silica or polystyrene microspheres for larger particles and monodisperse silica nanoparticles for smaller particles. Various types of fibrous films were produced depending on the properties of the dispersing medium, the effects of additives, and the compositions of the bidisperse colloids. When polystyrene microspheres were used as sacrificial templates, macropores were left behind in the nanofibers during the removal of polystyrene microspheres by calcination. The nonwoven films of electrospun nanofibers, which were decorated with silica microspheres or macropores, could be continuously produced with considerable ease under a relatively wide range of operating conditions. The surface properties of the films were characterized by contact angle measurement and an X-ray photoelectron spectrometer. Through the surface modification of the electrospun nanofibers with fluorinated silane coupling agents, superhydrophobic surfaces with low sliding angles were successfully prepared.

The color tuning behavior and switching stability of an electrically tunable colloidal photonic crystal system were studied with particular focus on the electrochemical aspects. Photonic color tuning of the colloidal arrays composed of monodisperse particles dispersed in water was achieved using external electric field through lattice constant manipulation. However, the number of effective color tuning cycle was limited due to generation of unwanted ions by electrolysis of the water medium during electrical switching. By introducing larger electrochemical potential window electrodes, such as conductive diamond-like carbon or boron-doped diamond, the switching stability was appreciably enhanced through reducing the number of ions generated.

Here, we demonstrate the preparation of a hybrid nanoplasmonic probe array, a nanoforest, which consists of gold nanostructures coated on top of silica nanospheres and evaporated gold film structure onto bottom through masks. Optically tunable plasmonic surfaces could be achieved by varying the nanoforest fabrication conditions, which acted as a selective nanoantenna. Plasmon coupling effects were effectively controlled by adjusting the vertical distance (nanogap) between the gold nanostructures on the silica bead and the bottom. Such control is critical to highly sensitive molecular detection applications. As a proof of concept, nanoforests were used as colorimetric sensors of refractive index changes. The sensors were highly sensitive and displayed distinct colors for small refractive index (RI) changes. The flexible and sensitive near/far-field optical properties render these nanoforests excellent plasmonic substrates for quantitative, sensitive and label-free sensing with nanoscale spatial resolution.

Hexagonally arranged plasmonic dot arrays were fabricated using simplified holographic lithography, electron-beam evaporation and lift-off processes. In our strategy, we used face-centered cubic structures as metal deposition masks which were created by prism holographic lithography. The features of plasmonic dot arrays such as arrangements, shapes, and sizes depended on the number of face-centered cubic structure layers and the laser exposure dose. The arrays showed tunable optical properties and were useful for surface-enhanced Raman scattering.

Photothermolysis technique via array of gold nanograils had been developed by illuminating near infrared laser light onto captured bacteria in metal nanostructure. The strong electromagnetic field enhancement at the sharp edges of the gold nanograils produced local heating that was sufficient to break the thick cell walls of the gram-positive Staphylococcus aureus cells within a short time. Individual cells in the nanograil array can be selectively lysed by adjusting the laser scanning area to the micrometer scale.

We have described a new and promising strategy for the fabrication of composite and porous photonic crystal microparticles that combines the self-assembly of colloidal particles with photolithography techniques. We fabricated silica/SU-8 composite microparticles with photonic bandgaps via four steps: (1) deposition of the silica colloidal crystals on the photoresist, (2) embedding of the colloidal crystals in the photoresist, (3) UV exposure through a photomask and subsequent development, and (4) release of the microparticles from the substrate. Embedding was performed above the glass transition temperature (T(g)) of uncrosslinked SU-8. At such temperatures, capillary forces on the silica particles facilitate the migration of colloidal crystals in the SU-8 matrix. Particle migration ceased when the top colloidal crystal layer was trapped at the interface between air and SU-8. In addition, we also prepared porous microparticles with an inverse opaline structure by dissolving the embedded silica particles from the composite structures. The porous microparticles showed enhanced reflectivity at the bandgap position due to the large refractive index contrast. The bandgap position of the microparticles was controlled by the size of the silica particles, which determined the lattice constant. Bilayered composite and porous microparticles with two distinct photonic bandgaps were also prepared by sequential deposition of colloidal crystals composed of two differently sized silica particles.

Colloidal particles are used as elemental building blocks to construct biofunctional nanostructures. In particular, multidimensional periodic arrangements of colloidal particles such as planar arrays and spherical assemblies can be used in a wide range of biological fields. The spatial regularity of such structures at the submicron-scale gives rise to special features such as a photonic bandgap (PBG) and selective permeability, which cannot be achieved by single colloidal particles. Recent advances in microfluidics technologies enable the fabrication of designed microparticles of equal size and shape in a continuous manner. Such microparticles have great potential for use in high-throughput screening and immunoassays. In this article, we review the current state-of-the-art in regard to colloidal assemblies and microparticles prepared by microfluidics for biological applications. This review consists of five main sections: (1) surface modification methods, (2) two dimensional (2D) and (3) three dimensional (3D) colloidal assemblies, (4) confined regular structures, and (5) novel fabrication strategies for advanced colloidal assemblies. In each section, we discuss not only the fabrication routes for biofunctional materials but also the characteristics of the materials and their biological applications. Finally, we outline the future perspectives for biofunctional colloidal materials.