Thick-film Devices Research Articles

A ternary organic solar cell with 300 nm thick active layer shows over 14% efficiency

In order to meet the requirements for making organic solar cells (OSCs) through solution printing techniques, great efforts have been devoted into developing high performance OSCs with relatively thicker active layers. In this work, a thick-film (300 nm) ternary OSC with a power conversion efficiency of 14.3% is fabricated by introducing phenyl-C61-butyric-acid-methyl ester (PC61BM) into a PBDB-T-2Cl:BTP-4F host blend. The addition of PC61BM is found to be helpful for improving the hole and electron mobilities, and thus facilitates charge transport as well as suppresses charge recombination in the active layers, leading to the improved efficiencies of OSCs with relatively thicker active layers. Our results demonstrate the feasibility of employing fullerene derivative PC61BM to construct a high-efficiency thick-film ternary device, which would promote the development of thick layer ternary OSCs to fulfill the requirements of future roll to roll production.

Copper–Cobalt Thermoelectric Generators: Power Improvement Through Optimized Thickness and Sandwiched Planar Structure

In this paper, metallic thermoelectric generators were studied and fabricated using copper (Cu) and cobalt (Co) as their respective positive and negative thermoelements. Thus, the chosen Cu-clad polyimide substrate alleviated the deposition of Cu and eased the microfabrication. A lateral device structure might assist in generating larger output power through its longer thermoleg length. Hence, the fabricated thick-film devices had planar and lateral structures with lateral heat flow and lateral thermopile layout. The strong correlations of electrical and thermal conductivities in metal thermoelements have resulted in lower Seebeck coefficient along with reduced thermoelectric power-generating performances. Alternatively, a thermoleg cross-sectional area ( ${A}$ ) optimization approach may optimize these disrupting correlations and improve their power-generating effectiveness, whereas a sandwiched planar structure can allow more thermopiles to be integrated without influencing the generator’s size. Both A optimization and sandwiched planar structure have rarely been applied and studied in the past works and have never been implemented using metal thermoelements. Hereafter, a Cu–Co device was enhanced through ${A}$ optimization by increasing the thickness of Co over 3.86 times the Cu thickness, and the implementations of a sandwiched planar structure. Herein, a flexible sandwiched planar thermoelectric generator was fabricated for the first time, using simpler microfabrication. This enhanced Cu–Co generator achieved a thermoelectric efficiency factor of ${6.6} \times {10}^{-{3}}\,\,\mu $ Wcm−2K−2( $12.89~\mu $ Wcm−2) at a temperature difference of 44.2 K. It remarked 3.1 times of improvement (by stacking three sets of thermopile) than its similar single Cu–Co thermopile of ten thermocouples.

Tuning the dipole moments of nonfullerene acceptors with an asymmetric terminal strategy for highly efficient organic solar cells

Fused-ring electron acceptors with asymmetric terminals for highly efficient thick-film photovoltaic devices.

Zero-Dimensional Cs2TeI6 Perovskite: Solution-Processed Thick Films with High X-ray Sensitivity

We demonstrate a potential candidate, the 0D “all-inorganic” perovskite material Cs2TeI6, as a sensitive all-inorganic X-ray photoconductor for the development of the new generation of direct photon-to-current conversion flat-panel X-ray imagers. Cs2TeI6 consists of high atomic number elements, has high electrical resistance, and exhibits high air and moisture stability, making it suitable as a sensitive X-ray photoconductor. In addition, we identify that Cs2TeI6 film can be prepared under a low-temperature process using electrostatic-assisted spray technique under atmospheric conditions and achieved resistivity of 4.2 × 1010 Ω·cm. The resulting air- and water-stable Cs2TeI6 device exhibits a strong photoresponse to X-ray radiation. An electron drift length on the order of 200 μm is estimated under an applied electrical field strength of 400 V·cm–1. A high sensitivity for Cs2TeI6 thick film device is realized, with the value of 192 nC·R–1cm–2 under 40 kVp X-rays at an electrical field of 250 V·cm–1, which...

Assessment of Ruthenium Dye N719 Adsorption Kinetics in Mesoporous TiO2 Films of Dye-Sensitized Solar Cells via Nanoplasmonic Sensing

A dye monolayer formation on a semiconductor surface is critical for efficient dye-sensitized solar cells. The role of dye is to absorb light and convert it to photoelectrons, which are injected into the semiconductor conduction band as device current. We measured dye N719 adsorption via optical techniques including indirect nanoplasmonic sensing. The adsorption rate constant of dye N719 in mimic TiO2 photoelectrodes is determined as ka = 983 M−1 s−1. Dye adsorption for ruthenium dyes N3, N749, and Z907, coated onto TiO2 photoelectrodes of varying thicknesses ranging from 3 μm to 10 μm, was conducted and related to fabricated dye-sensitized solar cell efficiency. Analytical studies included scanning electron microscopy and ellipsometry, X-ray diffraction, and UV-Vis spectroscopy, as well as quantum efficiency and current-voltage device characterizations. The results show greatest enhancement of device performance for dye N719 in spite of multilayer formation, which often is underestimated when addressing the dynamic competing factors that reverse thick-film device performance.

Copper–Nickel and Copper–Cobalt Thermoelectric Generators: Power-Generating Optimization through Structural Geometrics

In this paper of thermoelectric generators, metals are used as the prospective thermoelectric materials or thermoelements on flexible copper (Cu)-clad polyimide substrate. The fabricated thick film generators have planar and lateral structures with lateral heat flow and lateral thermopile layout. Hereby, two prototypes of thermoelectric generators are made, the first employing Cu and nickel (Ni) and the second Cu and cobalt (Co) as their positive and negative thermoelements, respectively. This paper also investigates the roles of geometrical structures such as the thermoleg’s length and width and the generator’s size in promoting elevated thermoelectric power generation. Consequently, the highest performing thermoleg designs (length: 5–20 mm; width: 100– $1000~\mu \text{m}$ ) for the two prototypes are identified as having a length, width, and thickness of 5 mm, $1000~\mu \text{m}$ , and $31~\mu \text{m}$ , respectively, with generator dimensions of 1.1 cm length and 4.3 cm width. Collectively, this design has an accumulated average temperature difference, output power density, and thermoelectric efficiency factor of 60 K, $0.59~\mu $ Wcm−2, and $1.64\times 10^{-\textsf {4}}\,\,\mu $ Wcm−2K−2, respectively, for the Cu–Ni generator, while the corresponding values for the Cu–Co generator are 64 K, $1.15~\mu $ Wcm−2, and $2.81\times 10^{-\textsf {4}}\,\,\mu $ Wcm−2K−2. An improvement factor of 1.71 is realized by the Cu–Co generator compared to the Cu–Ni one due to its larger Seebeck coefficient and figure of merit. This highlights the Cu–Co metallic couple as an encouraging thermoelement in thermoelectricity. Promisingly, the thick film and lateral device structures are more compatible and favorable for metal-based thermoelectric generators.

Analysis of the characteristics of thick-film NTC thermistor devices manufactured by screen-printing and firing technique and by room temperature aerosol deposition method (ADM)

The study compares thick-film NTC thermistor devices, produced by the screen-printing (and firing) technique and by the Aerosol Deposition Method (ADM) at room temperature. The devices are compared with respect to film quality (optical, mechanical) and to the negative temperature coefficient of resistance (NTCR) parameters [Formula: see text] and [Formula: see text]. While the screen-printed films are porous, the Aerosol Deposited (AD) films are characterized by high tightness, mechanical stability, and a production at room temperature. The electrical analysis shows that the AD films reach the [Formula: see text]- and [Formula: see text]-values of bulk NTCRs from literature after a moderate tempering step below 400[Formula: see text]C in air. The screen-printed films show [Formula: see text]-values that are comparable to the values of bulk NTCRs from literature and [Formula: see text]-values that are significantly higher.

A universal approach to improve electron mobility without significant enlarging phase separation in IDT-based non-fullerene acceptor organic solar cells

An in-situ solvent annealing method of solvent annealing during spin-coating (SC-SVA) was deployed to increase the electron mobility by improving the crystallinity of non-fullerene acceptor without significant enlarging the domain size. Although similar effect can be achieved by the post solvent annealing and co-solvents methods, these methods meanwhile enlarge the phase separation in the PTB7-Th:ITIC based organic solar cells. Thus, the efficiency of SC-SVA based device results in a 20% enhancement and exhibits a better photovoltaic performance than that of the post solvent annealing and co-solvents methods. The fundamental mechanism of these three methods were analyzed and discussed in detail. As the enhanced crystallinity of non-fullerene acceptor could improve charge carrier mobility, the thick-film devices with SC-SVA were fabricated and exhibit great photovoltaic performance. Moreover, this beneficial SC-SVA method was successfully employed in the other IDT-based PTB7-Th:ITIC-Th and PTB7-Th:IEIC devices as well as in the PTZ1:IDIC binary and PTZ1:IDIC:ITIC ternary devices. The high efficiencies of 10.11% and 10.30% were achieved for the binary and ternary devices with SC-SVA, respectively, showing its excellent universality and prospect.

Design of Donor Polymers with Strong Temperature-Dependent Aggregation Property for Efficient Organic Photovoltaics.

Bulk heterojunction (BHJ) organic solar cells (OSCs) have attracted intensive research attention over the past two decades owing to their unique advantages including mechanical flexibility, light weight, large area, and low-cost fabrications. To date, OSC devices have achieved power conversion efficiencies (PCEs) exceeding 12%. Much of the progress was enabled by the development of high-performance donor polymers with favorable morphological, electronic, and optical properties. A key problem in morphology control of OSCs is the trade-off between achieving small domain size and high polymer crystallinity, which is especially important for the realization of efficient thick-film devices with high fill factors. For example, the thickness of OSC blends containing state-of-the-art PTB7 family donor polymers are restricted to ∼100 nm due to their relatively low hole mobility and impure polymer domains. To further improve the device performance and promote commercialization of OSCs, there is a strong demand for the design of new donor polymers that can achieve an optimal blend morphology containing highly crystalline yet reasonably small domains. In this Account, we highlight recent progress on a new family of conjugated polymers with strong temperature-dependent aggregation (TDA) property. These polymers are mostly disaggregated and can be easily dissolved in solution at high temperatures, yet they can strongly aggregate when the solution is cooled to room temperature. This unique aggregation property allows us to control the disorder-order transition of the polymer during solution processing. By preheating the solution to high temperature (∼100 °C), the polymer chains are mostly disaggregated before spin coating; as the temperature of the solution drops during the spin coating process, the polymer can strongly aggregate and form crystalline domains yet that are not excessivelylarge. The overall blend morphology can be optimized by various processing conditions (e.g., temperature, spin-rates, concentration, etc.). This well-controlled and near-optimal BHJ morphology produced over a dozen cases of efficient OSCs with an active layer nearly 300 nm thick that can still achieve high FFs (70-77%) and efficiencies (10-11.7%). By studying the structure-property relationships of the donor polymers, we show that the second position branched alkyl chains and the fluorination on the polymer backbone are two key structural features that enable the strong TDA property. Our comparative studies also show that the TDA polymer family can be used to match with non-fullerene acceptors yielding OSCs with low voltage losses. The key difference between the empirical matching rules for fullerene and non-fullerene OSCs is that TDA polymers with slightly reduced crystallinity appear to match better with small molecular acceptors and yield higher OSC performances.

Toward Novel Wearable Pyroelectric Temperature Sensor for Medical Applications

Knowledge of an amputees’ residual limb skin temperature is considered to be of particular importance as an indicator of tissue health. Temperature within the prosthetic socket typically varies over the range 25 °C to 35 °C and this warm, confined environment causes sweating which creates favourable conditions for both the growth of bacteria and an increased risk of tissue breakdown. With this in mind a wearable sensor for the real-time measurement of temperature variations at the prosthetic socket/liner interface is under development and a proof of concept prototype is presented. The sensor exploits the large pyroelectric effect present in ferroelectric lead zirconate titanate PbZr x (Ti(1– x ))O3 (PZT) and has several inherent advantages over other methods of temperature sensing. The sensing element is a low cost commercially available thick-film PZT device. Mathematical models are developed to describe the sensor immitance and response to temperature change, and both the clamped and unclamped capacitances are investigated over the range 20 °C to 40 °C. Sensor characteristics were found to be dominated by the clamped dielectric constant and operation under short-circuit conditions is found to offer a constant sensor gain over the temperature range of interest.

Photon‐Pair Generation with a 100 nm Thick Carbon Nanotube Film

Nonlinear optics based on bulk materials is the current technique of choice for quantum-state generation and information processing. Scaling of nonlinear optical quantum devices is of significant interest to enable quantum devices with high performance. However, it is challenging to scale the nonlinear optical devices down to the nanoscale dimension due to relatively small nonlinear optical response of traditional bulk materials. Here, correlated photon pairs are generated in the nanometer scale using a nonlinear optical device for the first time. The approach uses spontaneous four-wave mixing in a carbon nanotube film with extremely large Kerr-nonlinearity (≈100 000 times larger than that of the widely used silica), which is achieved through careful control of the tube diameter during the carbon nanotube growth. Photon pairs with a coincidence to accidental ratio of 18 at the telecom wavelength of 1.5 µm are generated at room temperature in a ≈100 nm thick carbon nanotube film device, i.e., 1000 times thinner than the smallest existing devices. These results are promising for future integrated nonlinear quantum devices (e.g., quantum emission and processing devices).

A thick-film impedancemetric carbon monoxide sensor using layered perovskite-type cuprate

Carbon monoxide (CO) is a very toxic gas that is easily produced by incomplete combustion. In this study, a thick-film impedancemetric CO sensor with layered perovskite-type oxides (La2-xA’xCu1-yB’yO4; A’=Sr, Ba, Ce; B’=Zr, x, y=0–0.2) was investigated. The oxides were synthesized by a polymer precursor method and used as receptor material for an impedancemetric CO sensor. Sensing properties of the thick-film devices prepared by a screen printing technique were investigated by the AC impedance method using an LCR meter at 300–600°C. It was found that the La1.9Ce0.1CuO4 thick-film device responded well to CO between 50 and 600ppm at 400°C, and 50Hz.

Evaluation of screen-printable type S (Pt-PtRh) thermocouples on different ceramic substrates

Abstract The application of thermocouples as temperature sensors has been well known and has already been established for many years. However, for classical thick-film technology using screen-printing and firing, no standardized solutions exist. The here-presented newly developed PtRh thick-film compositions (90% Pt,10% Rh) allows to construct thick-film type S thermocouples (Pt/PtRh), following the IEC temperature characteristics. They can be fired in air, and therefore can be easily integrated into existing thick-film components and devices. In an earlier study, the new Pt-Rh composition was successfully tested on alumina substrates. Their electrical characteristics is equal with classical wire type S thermocouples. This study continues the investigations of thick-film thermocouples. We tested the newly developed pastes for high temperature applications on alumina substrates and evaluated the application of the new screen-printable type S thermocouples on LTCC ceramics. Three possible configurations were investigated: deposited on already fired LTCC substrates (post-fired), screen-printed and co-fired with LTCC tapes on the top surface as well as as buried structures. The paper presents the results of our evaluation and discusses further possible applications.

Humidity Sensing and Photodetection Behavior of Electrochemically Exfoliated Atomically Thin-Layered Black Phosphorus Nanosheets.

Recent investigations on two-dimensional black phosphorus material mainly highlight work on few atomic layers and multilayers. It is still unknown if the black phosphorus atomically thin sheet is an ideal structure for the enhanced gas-solid interactions due to its large surface area. To further investigate this concern, we have synthesized few atomic layer thick nanosheets of black phosphorus using an electrochemical exfoliation method. The surface morphology and thickness of the nanosheet were identified using AFM, TEM, and Raman spectroscopy. The black phosphorus nanosheet thick film device was used for the gas sensing application with exposure to different humidites. Further, the few layer black phosphorus nanosheet based transistor shows good mobility and on/off ratio. The UV light irradiation on the black phosphorus nanosheet shows good response time. The overall results show that the few layer thick film of black phosphorus nanosheets sample exhibits creditable sensitivity and better recovery time to be used in humidity sensor and photodetector applications.

The effects of crystallite size, surface area and morphology on the sensing properties of nanocrystalline SnO2 based system

Phase pure SnO2 powder, containing 0.25wt% Sb2O3 and 5wt% Pd was synthesized by sonication assisted simultaneous precipitation method. The as-prepared dry powder and those calcined at various temperatures (200–1000°C) were characterized by thermal analysis, x-ray diffraction (XRD), transmission electron microscopy (TEM) and surface area (BET) measurements. The effect of calcination temperature on morphology and crystal structure was investigated. The characterization results were employed to rationalize the catalytic sensing behavior towards n-butane gas of nanocrystalline SnO2 based material incorporated into a thick film device, which detects gas molecules and produces an electrical signal with a magnitude proportional to the concentration of the gas. The powder calcined at 200°C, having the lowest particle size (~14nm) exhibited the maximum sensitivity (~96%) at 400°C operating temperature with very fast response and recovery times suggesting their suitability for development of butane sensors/monitors.

Flexible, textronic temperature sensors, based on carbon nanostructures

Abstract The paper presents a comparative analysis of two types of flexible temperature sensors, made of carbon-based nanostructures composites. These sensors were fabricated by a low-cost screen-printing method, which qualifies them to large scale, portable consumer electronic products. Results of examined measurements show the possibility of application for thick film devices, especially dedicated to wearable electronics, also known as a textronics. Apart from general characterisation, the influence of technological processes on specific sensor parameters were examined, particulary the value of the temperature coefficient of resistance (TCR) and its stability during the device bending.

Integrated Powder-Based Thick Films for Thermoelectric, Pyroelectric, and Piezoelectric Energy Harvesting Devices

Energy harvesting devices based on piezoelectric, pyroelectric, and thermoelectric materials offer an attractive solution for batteryless and wireless sensor nodes for a range of sensor applications. Current devices are typically fabricated using semimanual approaches leading to higher costs and reduced yields as well as significant material wastage. Powder-based thick film devices have been shown to be capable of harvesting milliwatt levels of power while the associated printing technologies offer commercially attractive fabrication solutions. This paper provides a review of examples of recent piezoelectric, pyroelectric, and thermoelectric powder-based thick film energy harvester devices and outlines potential fabrication techniques, ink compositions, and ways to reduce processing temperatures that can be used to create integrated thick film energy harvesting devices. The key to the creation of such devices is the management of thermal budgets and processing environments to ensure the functional properties of the thick films are maximized.

Impedancemetric acetylene gas sensing properties of Sm–Fe-based perovskite-type oxide-based thick-film device

Perovskite-type Sm1−xCaxFeO3 (x=0, 0.05, 0.20, 0.50, 0.75, 1.0) powders as sensor materials were prepared by a wet-chemical route using a polymer precursor method at 750°C. A perovskite-type oxide thick-film device prepared by a screen-printing method was used for an acetylene (C2H2) sensor for which outputs were measured by AC impedance spectroscopy at 400°C. Although sensitivities of the devices using oxides with Ca2+ substitution were decreased because of reduction in the amount of impedance change between air and sample gas, the device without Ca2+ substitution showed extremely high response at a low frequency. According to Nyquist's plots of the SmFeO3 device, this is attributed to the fact that impedance of charge transfer from the surface reaction was taken at a low frequency. It was also found that the sensor devices showed good selectivity to interference gases.

Pt-TiO2/MWCNTs Hybrid Composites for Monitoring Low Hydrogen Concentrations in Air

Hydrogen is a valuable fuel for the next energy scenario. Unfortunately, hydrogen is highly flammable at concentrations higher than 4% in air. This aspect makes the monitoring of H2 leaks an essential issue for safety reasons, especially in the transportation field. In this paper, nanocomposites based on Pt-doped TiO2/multiwalled carbon nanotubes (MWCNTs) have been introduced as sensitive materials for H2 at low temperatures. Pt-TiO2/MWNTs nanocomposites with different composition have been prepared by a simple wet chemical procedure and their morphological, microstructural and electrical properties were investigated. Resistive thick-film devices have been fabricated printing the hybrid nanocomposites on alumina substrates provided with Pt interdigitated electrodes. Electrical tests in air have shown that embedding MWCNTs in the TiO2 matrix modify markedly the electrical conductivity, providing a means to decrease the resistance of the sensing layer. Pt acts as a catalytic additive. Pt-TiO2/MWNTs-based sensors were found to be sensitive to hydrogen at concentrations between 0.5 and 3% in air, satisfying the requisites for practical applications in hydrogen leak detection devices.

Low-Power-Consumption Metal Oxide NO2 Gas Sensor Based on Micro-Heater and Screen Printing Technology

An NO2 micro gas sensor was fabricated based on a micro-heater using tin oxide nano-powders for effective gas detection and monitoring system with low power consumption and high sensitivity. The processes of the fabrication were acceptable to the conventional CMOS processes for mass-production. Semiconducting SnO2 nano-powders were synthesized via the co-precipitation method; and to increase the sensitivity of the NO2 gas rare metal dopants were added. In the structure of the micro-heater, the resistances of two semi-circular Pt heaters were connected to the spreader for thermal uniformity. The resistance of each heater becomes an electrically equal Wheatstone-bridge, which was divided in half by the heat spreading structure. Based on the aforementioned design, a low-power-consumption micro-heater was fabricated using the CMOS-compatible MEMS processes. A bridge-type micro-heater based on the Si substrate was fabricated via surface micro-machining. The NO2 sensing properties of a screen-printed tin oxide thick film device were measured The micro gas sensors showed substantial sensitivity down to 0.5 ppm NO2 at a low power consumption (34.2 mW).