Thermodynamically tuned zirconia thin films are fabricated for diverse Urbach energies in a homogeneous condensed system. In the analysis, the electrical breakdown of zirconia thin films is ascribed ...to the tunneling‐driven electron propagation involving virtual photons. An externally applied electric field is considered to expand the Urbach‐energy‐characterized energy distribution of sub‐bandgap states into their spatial distribution. In this expansion, the virtual‐photon energies activate the tunneling‐driven electron propagation through localized observer states. The integral of the virtual‐photon energies over the entire tunneling path is equal to the initial energy barrier.
Amorphous zirconia thin films, thermodynamically tuned for diverse Urbach energies, are prepared via solution process. Correlations between the distribution of states, the presence of defects, and the behavior of electrons are investigated. Lastly, the electrical breakdown in zirconia films is explained with consideration of the tunneling‐driven electron propagation involving virtual photons.
The lifetime of a device depends highly on that of its battery. In order to enhance the longevity of microsystems or sensor networks, it is necessary for these devices to be self‐powered. Indoor ...photovoltaics allow the possibility of harvesting artificial light sources for powering microsystems. Whereas indoor photovoltaics based on single active layers have showed high efficiencies under LED lighting, tandem structures have yet to be tested extensively. In our study, we use finite‐difference time‐domain simulations to study the highest possible short‐circuit current density that can be extracted from tandem organic devices. We compare the simulation results to the results for photovoltaic devices based on single bulk active layer heterojunctions. Our simulations found that although detailed balanced band gap calculations show tandem photovoltaics to be viable, the low‐intensity emission spectra of white LED light sources can be better harvested by single active layer‐based photovoltaics. The current‐matching limitation of a tandem photovoltaic structure connected in series limits the highest output current and open‐circuit voltage of the device and, thus, its performance for the illumination of lower intensity light.
Organic tandem solar cell with the active materials having optimized band gap and thickness is tested under low‐intensity indoor light. The current‐matching limitation of a tandem photovoltaic structure connected in series limits the highest output current and open‐circuit voltage at low‐intensity light. Therefore, the tandem solar cell constructed with active materials having optimized band gaps and thicknesses is less efficient than single‐celled photovoltaic device for indoor application.
Novel, low‐voltage, high‐detectivity, solution‐processed, flexible near‐infrared (NIR) photodetectors for optoelectronic applications are realized and their optoelectronic properties are investigated ...for the first time. This is achieved by synthesizing Ag2Se nanoparticles (NPs) in aqueous solutions, and depositing highly crystalline Ag2Se thin films at 150 °C with redistributed Ag2Se NPs in aqueous inks. The high conductivity and low trap concentration of the 150 °C annealed Ag2Se films result from the Ag formed inside the films and the improved film quality, respectively. These factors are both critical for the realization of high‐performance flexible photodetectors. The fabricated device exhibits a high detectivity of 7.14 × 109 Jones (above 1 × 109) at room temperature, delivering low power consumption. This detectivity is superior to those of reported low band‐gap semiconductor systems, although the device has undergone 0.38% compressive and tensile strains. Moreover, the performance of the device is better than that of MoS2‐based phototransistors, black arsenic phosphorus field‐effect transistors, or commercial thermistor bolometers at room temperature (D* ≈ 108 Jones), and is exposed to mid‐infrared light.
Synthesized Ag2Se nanoparticles are employed to realize high‐performance flexible near‐infrared photodetectors. The fabricated flexible photodetectors, consisting of 150 °C annealed Ag2Se films, exhibit excellent performance and flexibility, and deliver a high detectivity of 7.14 × 109 Jones (above 1 × 109) at room temperature.
We propose a feasible method of manipulating the surface energy of crosslinked poly(4-vinylphenol) (c-PVP) thin films through the surface compositional modification assisted by an etchant. A physical ...picture of the surface-energy manipulation of c-PVP thin films based on the surface-selective molecular subtractive approach is clarified by investigating the chemical composition of the c-PVP film surfaces. We reveal that the molecular detachment by solvation on the surface leads to a reduction in the surface PVP density, thereby decreasing residual hydroxyl groups on the surface. In particular, it is found that the surface energy of a c-PVP thin film can be controlled by exploiting the thermal-treatment-time dependence of the soluble-PVP density. Organic thin-film transistors (TFTs) are fabricated via a solution process for demonstrating the applicability of our surface-energy-engineered c-PVP film as a gate insulator. The TFTs with the engineered c-PVP gate insulators exhibit improved electrical characteristics, compared to those with ordinary c-PVP gate insulators.
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•We propose a method for the surface-energy manipulation of a c-PVP thin film.•Surface-selective molecular detachment occurs with aid of an etchant.•The surface energy is manipulated exploiting the density-controllable soluble PVP.•The surface-energy engineering leads to the improvement of TFT characteristics.
Abstract Biosensors have emerged as vital tools for the detection and monitoring of essential biological information. However, their efficiency is often constrained by limitations in the power ...supply. To address this challenge, energy harvesting systems have gained prominence. These off‐grid, independent systems harness energy from the surrounding environment, providing a sustainable solution for powering biosensors autonomously. This continuous power source overcomes critical constraints, ensuring uninterrupted operation and seamless data collection. In this article, a comprehensive review of recent literature on energy harvesting‐based biosensors is presented. Various techniques and technologies are critically examined, including optical, mechanical, thermal, and wireless power transfer, focusing on their applications and optimization. Furthermore, the immense potential of these energy harvesting‐driven biosensors is highlighted across diverse fields, such as medicine, environmental surveillance, and biosignal analysis. By exploring the integration of energy harvesting systems, this review underscores their pivotal role in advancing biosensor technology. These innovations promise improved efficiency, reduced environmental impact, and broader applicability, marking significant progress in the field of biosensors.
Hardware neural networks with mechanical flexibility are promising next‐generation computing systems for smart wearable electronics. Several studies have been conducted on flexible neural networks ...for practical applications; however, developing systems with complete synaptic plasticity for combinatorial optimization remains challenging. In this study, the metal‐ion injection density is explored as a diffusive parameter of the conductive filament in organic memristors. Additionally, a flexible artificial synapse with bio‐realistic synaptic plasticity is developed using organic memristors that have systematically engineered metal‐ion injections, for the first time. In the proposed artificial synapse, short‐term plasticity (STP), long‐term plasticity, and homeostatic plasticity are independently achieved and are analogous to their biological counterparts. The time windows of the STP and homeostatic plasticity are controlled by the ion‐injection density and electric‐signal conditions, respectively. Moreover, stable capabilities for complex combinatorial optimization in the developed synapse arrays are demonstrated under spike‐dependent operations. This effective concept for realizing flexible neuromorphic systems for complex combinatorial optimization is an essential building block for achieving a new paradigm of wearable smart electronics associated with artificial intelligent systems.
Flexible hardware neural networks for complex combinatorial optimization are demonstrated utilizing the organic memristor‐based artificial synapses. In the proposed synapse, metal‐ion injections are systematically engineered, which leads to the bio‐realistic synaptic plasticity. The developed systems are reliably trained and computed for combinatorial optimization such as the complex max‐cut problems.
The optical characteristics of nanoparticles will vary according to particle size. With decrease in the size of the nanoparticle (NP), the bandgap of the material increases, thus providing a ...blue-shift in the refractive index of the material. In this study, we analyzed the effect of different sized zinc oxide (ZnO) nanoparticle optical spacer on the ideal short-circuit current density (Jsc,ideal) of an hybrid photovoltaic cell. ZnO was used as an optical spacer in the solar cell structure to improve the light absorbed in the active layer. Refractive index and extinction coefficient of different sized ZnO nanoparticles were calculated using tight binding model. We implemented these results in two different morphological models: nanoparticle model, and thin-film model. In the nanoparticle model, the ZnO NPs were considered as nanospheres which scatter the incoming light. Comparison of these models helped us to evaluate the improvement in the Jsc,ideal due to scattering effects from nanoparticles. Finally, the optimized structure was obtained for different active layer thicknesses by varying the thickness of the ZnO layer.
•Refractive index of ZnO nanoparticles is size-dependent.•Optical spacer's ZnO nanoparticles' size affects the light absorption.•Two morphological FDTD models, nanoparticle spheres 3D model, and thin-film 1D model.•The optimized structure was obtained by varying the thickness of the ZnO layer.
With increasing demand for wearable electronics capable of computing huge data, flexible neuromorphic systems mimicking brain functions have been receiving much attention. Despite considerable ...efforts in developing practical neural networks utilizing several types of flexible artificial synapses, it is still challenging to develop wearable systems for complex computations due to the difficulties in emulating continuous memory states in a synaptic component. In this study, polymer conductivity is analyzed as a crucial factor in determining the growth dynamics of metallic filaments in organic memristors. Moreover, flexible memristors with bio‐mimetic synaptic functions such as linearly tunable weights are demonstrated by engineering the polymer conductivity. In the organic memristor, the cluster‐structured filaments are grown within the polymer medium in response to electric stimuli, resulting in gradual resistive switching and stable synaptic plasticity. Additionally, the device exhibits the continuous and numerous non‐volatile memory states due to its low leakage current. Furthermore, complex hardware neural networks including ternary logic operators and a noisy image recognitions system are successfully implemented utilizing the developed memristor arrays. This promising concept of creating flexible neural networks with bio‐mimetic weight distributions will contribute to the development of a new computing architecture for energy‐efficient wearable smart electronics.
Flexible neuromorphic systems for complex computations are implemented using organic memristors with bio‐mimetic synaptic weights. In the device, the cluster‐structured filaments are achieved by optimizing the polymer conductivity, which leads to the continuous memory states. The systems showed stable computing performances including ternary logic operators and noisy image recognition systems.
We demonstrate a dimethyl ketone treatment to produce a hydrophobic surface of cross-linked poly(4-vinylphenol) (c-PVP) insulators for pentacene thin-film transistors (TFTs). Through water contact ...angle measurements, the dimethyl ketone treatment is proven to significantly increase the surface hydrophobicity of c-PVP films. The results of X-ray diffraction analyses indicate that the dimethyl ketone-treated c-PVP insulator contributes to enhancing the crystallinity of pentacene films and reducing the density of lamellar grains and bulk phase crystallites in pentacene films. In addition, the growth of lamellar grains is elucidated by examining the initial growths of the pentacene films on the c-PVP films with different surface energies. Consequently, the enhancement in the performance of pentacene TFTs is achieved by incorporating the dimethyl ketone-treated c-PVP films as gate insulators.
We demonstrate a dimethyl ketone treatment for structural modification of cross-linked poly(4-vinylphenol) (c-PVP) gate insulator in pentacene thin-film transistors (TFTs). Here, the dimethyl ketone ...treatment was performed immediately after spin-coating the insulator solution, followed by thermal annealing for cross-linking of PVP molecules. It is found that the dimethyl ketone treatment lowered the surface energy of the PVP gate insulator and made the PVP film thinner. The results of X-ray diffraction and atomic force microscopy analyses showed that the dimethyl ketone-treated c-PVP insulator contributes to enhancing the crystallinity of pentacene semiconductor films and reducing the density of lamellar grains and bulk phase crystallites in pentacene films. Consequently, the performance improvement of the pentacene TFT is achieved by structurally modifying the c-PVP gate insulator through the dimethyl ketone treatment.
