Proof Of Concept Device Research Articles

Exploring the potential of powder-to-film processing for proof-of-concept BaZrS3 perovskite solar cells

Lead-free chalcogenide perovskites, such as BaZrS3, manifest as strong candidates to replace toxic metals-containing halide perovskites in optoelectronic applications, but the formation of high-quality films for photovoltaic applications remains a major challenge for now, since very high temperatures are needed to fully crystalize the compound. To circumvent this issue, liquid-phase synthesis, through direct fabrication of perovskite nanocrystals dispersed in an organic solvent or a conversion of a pre-crystalline powder to an ink, has been suggested as a viable strategy for low-temperature processing. However, both cases result in films which cannot be used in the fabrication of solar cells. Herein, in this work, we adopt the latter approach, and convert BaZrS3 particles, from solid-state synthesis to a stable colloidal dispersion in a Ν-Methyl-2-pyrrolidone (NMP)-oleylamine (OA) mixture. We report a detailed identification of the structural changes of this transformation with a large range of crystallographic, spectroscopic and microscopic techniques. Then, we evaluate the feasibility of the process for the fabrication of films. BaZrS3 infiltrated in mesoporous TiO2/FTO transparent glass substrates were used as photolectrodes in solar cells and proof-of concept devices were constructed in conjunction with I3-/I- redox electrolyte for the first time in literature, reaching a mean PCE of 0.11% and a FF of 61%. We believe that this work will pave the way towards the systematic use of BaZrS3 (or other similar chalcogenide perovskites) in solar cells and other relevant optoelectronic devices.

Solid state thermal rectification by chemical pressure tuning of magnetic properties in perovskites

From an efficiency framework, waste heat generation and accumulation place significant limitations on how systems ultimately perform. Particularly, heat buildup leads to a significant loss of efficiency and subsequently system failure. In addition, current insulation and heat removal elements for supporting reliability and efficiency are robust and high power consumption systems that are based entirely on linear thermal elements instead of non-linear elements that would allow a unidirectional heat regulation process, thereby avoiding heat accumulation. In this sense, thermal rectifiers have recently attracted considerable interest due to their ability to manage heat unidirectionally. In this work, with the aim of exploring the potential of perovskites in thermal rectification, the magnon mediated thermal transport in the system La0.7Sr0.3Mn1–xCoxO3 (0 < x < 0.1) obtained by the solid-state ceramic route is investigated. Interestingly, results shows that thermal conductivity and Curie temperature substantially decreases with increasing of Co contents, which is attributed to the fact that positive chemical pressure is created due to smaller Co atoms take the place of some of the Mn atoms in the perovskite, shrinking the crystal structure. Taking advantage of those granted features, two-segment thermal diodes based on La0.7Sr0.3Mn1–xCoxO3/SiO2 have been implemented as a proof of concept devices. Experimental thermal transfer characteristics reveal that thermal diodes have markedly a nonlinear heat transport with rectification factors up to 2.3, meaning that devices control the heat flow via the deactivation of magnons through the Curie temperature; which in turn, controls accurately the on state of the device.

2D materials-enabled optical modulators: From visible to terahertz spectral range

Two-dimensional (2D) materials with layered structures have a variety of exceptional electronic and optical attributes for potentially developing basic functions of light wave technology from light-emitting to -modulating and -sensing. Here, we present state-of-the-art 2D materials-enabled optical intensity modulators according to their operation spectral ranges, which are mainly determined by the optical bandgaps of the 2D materials. Leveraging rich electronic structures from different 2D materials and the governed unique light–matter interactions, the working mechanisms and device architectures for the enabled modulators at specific wavelength ranges are discussed. For instance, the tunable excitonic effect in monolayer transition metal dichalcogenides allows the modulation of visible light. Electro-absorptive and electro-refractive graphene modulators could be operated in the telecom-band relying on their linear dispersion of the massless Dirac fermions. The bendable electronic band edge of the narrow bandgap in few-layer black phosphorus promises the modulation of mid-infrared light via the quantum-confined Franz–Keldysh or Burstein–Moss shift effect. Electrically and magnetically tunable optical conductivity in graphene also supports the realizations of terahertz modulators. While these modulators were demonstrated as proof of concept devices, part of them have great potential for future realistic applications, as discussed with their wavelength coverage, modulation depth, insertion loss, dynamic response speed, etc. Specifically, benefiting from the well-developed technologies of photonic chips and optical fibers in telecom and datacom, the 2D materials-based modulators integrated on these photonic structures are expected to find applications in fiber and chip optical communications. The free-space mid-infrared and terahertz modulators based on 2D materials can expect application in chemical bond spectroscopy, free-space communications, and environment/health sensing.

Mechanoluminescence spectrum tuning from zinc sulfide and all-inorganic perovskite quantum dots composite

Mechanoluminescence (ML) materials exhibit great potential in the fields of light sources, displays, and stress sensors because they can convert mechanical stimuli into luminescence. Most ML materials exhibit weak brightness and limited colors; therefore, tunable colors are highly desired. Herein, a facile strategy for tuning the ML of a flexible composite of zinc sulfide (ZnS) phosphor and all-inorganic CsPbX3 (X = Cl, Br, and I) perovskite quantum dots (PeQDs) is demonstrated. A broad color expression with a narrow emission band was achieved under low stretching–releasing stress by changing the halide component of CsPbX3. The color conversion between ZnS and PeQDs is a radiative combination and reabsorption process, and full color tuning from 510 to 710 nm occurred because of the bandgap tailoring of PeQDs. Furthermore, some proof-of concept devices, including multicolor displays and white light sources, were demonstrated by changing the composition of PeQDs. This work provides a versatile approach to fine–tune the ML spectrum, thereby paving the way for applications such as piezophotonic displays and white light sources.

Recyclable and Flexible Dual-Mode Electronics with Light and Heat Management.

Realizing multiple functions and sustainable manufacturing within the same electronic device would be highly attractive from a design and fabrication perspective. Here we demonstrate a recyclable dual-mode thin-film device that can perform both light emission and heat management simultaneously. The device is composed of a dissolvable emitting layer sandwiched between two undissolvable conducting films. The vertical multilayered device enables a highly flexible and foldable multicolor electroluminescent emission ranging from yellow or blue to white, and the coplanar monolayered conductor achieves tunable Joule heat temperature setting. By utilizing selective dissolution and artificial reconstruction of each layered component, the parent device shows full recyclability and reconstructability without severe performance degradation after several recycles. The proof-of concept device provides an ideal strategy to construct a multifunctional film system with recyclability and makes a significant contribution to scientific and technological advancement in low-cost sustainable electronics and optoelectronics.

Enhanced performance nanostructured thermoelectric converter for self-powering health sensors

Abstract Grain boundaries (Gbs) in polycrystals control the boundary-scattering in the intergranular transport of phonons and electrons, therefore Gbs represent a key design factor for enhancing the thermoelectric properties in polycrystals. Here, extended energy barriers have been created via grain coating by the segregation of 10 nm average thick graphene nanoplatelets (GNps) at the Gbs of N-type and P-type Bi2Te3 thermoelectric polycrytals. By realizing a proof-of concept device, a ZT~1.5 at room temperature has been achieved in comparison to the reference one with ZT~0.9, which represents an increment of around 35% on the maximun output power of the device.The improvement on ZT is mainly related to the enhancement of the thermoelectric power S2σ, as well as the impoverishment of the thermal conductivity k of the materials. Hence, energy barrier extension at Gbs may be an appropriate strategy to filter away low-energy carriers via energy filtering, and thereby to increase ZT. Besides, the thermoelectric converter is able to efficiently harvest heat from temperature gradients as low as 10 °C coming from the human body. Consequently, based on the results, the present research shed a light for the development of self-powering health sensors devices from human body heat which would eliminate the need for batteries, as well as to ensure their long-term powering.

Cavity-enhanced detection of transient absorption signals

We present a simple, high-duty-cycle, cavity-enhanced optical absorption measurement technique based on delay-limited Pound-Drever-Hall (PDH) sideband locking. The chosen circuit naturally provides realtime readout of the amplitude quadrature of the PDH error signal, which can be mapped onto the cavity’s internal loss rate while using the phase quadrature to lock sideband frequency to the cavity mode. Our proofof-concept device comprises a 5-cm-long Fabry-Perot cavity with a 450 kHz bandwidth (finesse 6800, 350 ns power ringdown), and a feedback bandwidth of several MHz, limited primarily by the group delay of our electronics. This technique could readily be applied to other optical resonators such as fiber cavities, with potential applications in radiation dosimetry.

Carrier selective metal-oxides for self-doped silicon nanowire solar cells

Selection of a material that serves multiple purposes is always beneficial for any electronic device including solar cells. This study investigates nickel oxide (NiO) as a multipurpose material to overcome the potential issues observed in traditional solar cells. A proof-of concept device is fabricated to understand the efficient hole transport from NiO while blocking electrons as determined by I-V measurements showing suppression of dark current and enhancement in the power conversion from the solar cell. Enhanced surface defects in the silicon nanowires (SiNWs) leading to the poor carrier collection is possible to be improved by the selection of wide bandgap metal-oxides that show high band offset for one carrier (electron/hole) while negligible band offset for another carrier (hole/electron) is discussed. Furthermore, Fermi level de-pinning for NiO sandwiched between different metal electrodes and SiNWs, signifying that the selection of appropriate metal electrodes is another key factor in improving the efficiency of solar cells; which is experimentally studied in this work. As fabricated solar cells in this work do not use high temperature diffused PN junction to separate the charge carriers neither toxic gases for doping SiNWs.

High Efficiency Multi-Level Flexible Triboelectric Nanogenerator for Wearable Electronics

With the rapid development of wearable electronics and sensor networks, batteries cannot meet the sustainable energy requirement due to their limited lifetime, size and degradation. With miniaturization leading to high-power and robustness, triboelectric nanogenerators(TENGs) have been conceived as a promising technology by harvesting mechanical energy to power small electronics and wearables. The main issues associated with TENGs are their very low output power leading to lower output charge density and high impedance matching. In this work, a state of the art multilayer flexible structure is devised which not only increases the charge density but also provides a high average power output. Thin-film organic flexible materials are deposited to acquire charges from the triboelectrification process, allowing the acceptance of more charges from an electrode and thereby increasing the power output. Material work function provide better understanding towards charge transfer process. A proof of concept device is conceptualized for use in a highly efficient self-powered sensor network system, converting ambient mechanical energy to electricity with a 1.2kV peak amplitude and a very high device performance. This device structure makes the TENGs attractive to charging applications for wearables and large-scale harvesting without massive volume. By this technique, we have overcome numerous friction-based operation challenges including lack of uniform contact, material loss through wear, high sensitivity to humidity, and output power storage. By considering these merits of simple fabrication, outstanding performance, robust characteristic and low-cost technology, we believe that multi level flexible TENGs can open great opportunities not only for powering small electronics but can contribute to large-scale energy harvesting through engineering design being complementary to existing energy sources.

Thermal rectification via sequential deactivation of magnons

Theoretically, a thermal rectifier is a solid state device which presents a greater heat flux in the forward than in the reverse thermal bias, Q+ &amp;gt; Q−. Ferromagnetic materials, which can exist in two magnetic states with distinct thermal conductivities, provide a unique opportunity to realize nonlinear thermal transport. Herein, by realizing a proof-of concept device consisting of manganites type La1-xSrxMnO3, we introduce a two-segment thermal diode that manipulates the heat via a sequential deactivation of magnons in each segment through their respective Curie temperatures Tc. Thermal measurements of the diode show that as the sequential magnetic transitions occur, the rectification factor increases. We interpret such an enhancement in the rectification factor due to drastic changes in the thermal conductance of the device as a consequence of the spin-disorder dominance above Tc. Furthermore, the results are validated via an analytical model within the framework of the Fourier law by using power law approximations of the temperature-dependent thermal conductivity of segments. Hence, sequential deactivation of magnons provides an alternative route so as to develop enhanced performance thermal rectifiers.

Sputtered SiC coatings for radiative cooling and light absorption

The outstanding thermomechanical and broadband spectral absorptance of silicon carbide (SiC) coatings makes it a promising material for high-performance optoelectronics devices and photothermal applications. We propose sputtered SiC coatings to develop: (i) broadband infrared emitters for passive radiative cooling and (ii) a spectrally selective ultrathin nanocomposite absorber. For radiative cooling, a proof of concept device has been fabricated by topping the as-sputtered 2.5-μm-thick SiC films with a single pair of distributed Bragg’s reflector (DBR). Owing to the infrared surface polariton resonances of SiC, broadband infrared emissivity of 0.8 is achieved in atmospheric transparency window (8 to 14 μm). The higher refractive index contrast (Δn) in DBR is achieved by depositing high refractive index dense Si film on top of low refractive index nanoporous SiO2, which was fabricated by oblique angle deposition approach. A single pair of DBR on top of SiC considerably reduces the absorption of the overall solar spectrum by 18%. In addition, impact of various materials and number of pairs of DBRs on radiative cooling are also numerically investigated. We also designed and fabricated SiC-based spectrally selective solar absorber coatings. An ultrathin SiC-based nanocomposite absorber with sandwich-like configuration consisting of SiC/Ag-SiC/SiC on reflective substrate has exhibited an outstanding absorptance of 91.24% in the wavelength range of 280 to 2000 nm. The surface plasmon polaritons of metal inclusion within the SiC matrix of an ultrathin nanocomposite (40 nm) layer has contributed to broadband light absorption, whereas the top most layer of SiC (40 nm) acts as antireflection layer. Conclusively, the versatility of sputtered SiC coatings has proven to be promising for radiative cooling and spectrally selective solar absorbers.

Temporal and Remote Tuning of Piezophotonic-Effect-Induced Luminescence and Color Gamut via Modulating Magnetic Field.

Light-emitting materials have been extensively investigated because of their widespread applications in solid-state lighting, displays, sensors, and bioimaging. In these applications, it is highly desirable to achieve tunable luminescence in terms of luminescent intensity and wavelength. Here, a convenient physical approach of temporal and remote tuning of light-emitting wavelength and color is demonstrated, which is greatly different from conventional methods. It is shown that by modulating the frequency of magnetic-field excitation at room temperature, luminescence from the flexible composites of ZnS:Al, Cu phosphors induced by the piezophotonic effect can be tuned in real time and in situ. The mechanistic investigation suggests that the observed tunable piezophotonic emission is ascribed to the tilting band structure of the ZnS phosphor induced by magnetostrictive strain under a high frequency of magnetic-field excitation. Furthermore, some proof-of concept devices, including red-green-blue full-color displays and tunable white-light sources are demonstrated simply by frequency modulation. A new understanding of the fundamentals of both luminescence and magnetic-optics coupling is thus provided, while offering opportunities in magnetic-optical sensing, piezophotonics, energy harvesting, novel light sources, and displays.

Enhanced performance thermoelectric module having asymmetrical legs

Key concepts like waste heat recycling or waste heat recovery are the basic ideas in thermoelectricity so as to the design the newest solid state sources of energy for a stable supply of electricity and environmental protection. According to several theoretical predictions; at device level, the geometry and configuration of the thermoelectric legs are crucial in the thermoelectric performance of the thermoelectric modules. Unlike to conventional geometry thermoelectric legs, asymmetrical (pyramidal) legs could help by lowering the overall thermal conductance of the device so as to increase the temperature gradient in the legs, as well as by harnessing the Thomson effect, which is generally neglected in conventional symmetrical (rectangular) thermoelectric legs. Curiously, experimental studies confirming the previous predictions have not been carried out so far, perhaps because of the existing constraints to fabricate thermoelectric legs with complex geometrical shapes. In this work, based on the promising enhancement of the thermoelectric performance in thermoelectric modules via legs with non-constant cross sections, it has been developed a novel design of a thermoelectric module having asymmetrical legs with truncated square pyramid shape, and by first time it has been validated experimentally its thermoelectric performance by realizing a proof-of concept device which shows to have almost twofold the thermoelectric figure of merit as compared to conventional one with a constant square cross section. Besides, the variables required to engineer enhanced performance thermoelectric devices are properly identified for use as power sources especially in low consumption portable devices. Therefore, the present results prove that geometrical configuration of the device legs can improve significantly the thermoelectric performance of the device.

Light-Induced Solubility Modulation of Polyfluorene To Enhance the Performance of OLEDs.

Liquid-phase processing is a key prerequisite for the cost-efficient fabrication of organic electronic devices. We report an approach for light-induced modulation of the solubility of π-conjugated polymers (polyfluorene) with side chains functionalized with hydroxycinnamic acid. Irradiation with light cleaves the solubilizing side chains and renders the thin films of the polyfluorene insoluble. In a proof of concept device, polyfluorenes were applied as emissive layers in OLEDs. Photoirradiation of the emission layer leads to an increase in OLED performance combined with a modulation of the solubility of the thin film. These results offer the possibility for further development in terms of manipulating the solubility and emissive parameters of an important class of functional materials.

Development of an ultrasonic airflow measurement device for ducted air.

In this study, an in-duct ultrasonic airflow measurement device has been designed, developed and tested. The airflow measurement results for a small range of airflow velocities and temperatures show that the accuracy was better than 3.5% root mean square (RMS) when it was tested within a round or square duct compared to the in-line Venturi tube airflow meter used for reference. This proof of concept device has provided evidence that with further development it could be a low-cost alternative to pressure differential devices such as the orifice plate airflow meter for monitoring energy efficiency performance and reliability of ventilation systems. The design uses a number of techniques and design choices to provide solutions to lower the implementation cost of the device compared to traditional airflow meters. The design choices that were found to work well are the single sided transducer arrangement for a “V” shaped reflective path and the use of square wave transmitter pulses ending with the necessary 180° phase changed pulse train to suppress transducer ringing. The device is also designed so that it does not have to rely on high-speed analogue to digital converters (ADC) and intensive digital signal processing, so could be implemented using voltage comparators and low-cost microcontrollers.

Highly insulating, fully porous silicon substrates for high temperature micro-hotplates

As alternative to established thermal substrates and thin membranes, we have investigated fully porous silicon substrates as highly insulating material for thermal devices. Exhibiting a thermal conductivity similar to silica glass and considerably lower than silicon nitride due to increased phonon scattering, thick mesoporous silicon also offers improved thermal and mechanical stability. Our work has focused on full wafer thickness porosification as a not extensively documented use of porous silicon and its application to thermal devices. Here we present measurement and finite element simulation results for our latest generation thin film microheaters on fully porous silicon substrates as proof of concept devices. Porosity, mass density, and specific heat capacity of porous silicon are deduced from fabrication parameters, thermal conductivity is determined by the so-called 3ω-measurement method, and all material properties are validated by fitting measurement data to our finite element models. For thick fully porous domains we estimated a thermal conductivity of ≈0.9W/m/K, as well as a density of ≈1200kg/m3, a specific heat capacity of ≈780J/kg/K and a corresponding volumetric porosity of ≈50%. Thin film fabrication of nitride passivation and molybdenum meander microheaters on fully porous domains allowed characterization of thermal performance and insulation. For 10mm2 microheaters we measured a power efficiency of 0.40K/mW stable up to a maximum temperature of 475°C, compared to 0.37K/mW stable up to 440°C on silica glass. Both static and dynamic heater measurements show superior performance of fully porous silicon substrates compared to reference samples on thin silica glass substrates.

Broad-band Mach-Zehnder interferometers as high performance refractive index sensors: theory and monolithic implementation.

Broad-band Mach-Zehnder interferometry is analytically described and experimentally demonstrated as an analytical tool capable of high accuracy refractive index measurements over a wide spectral range. Suitable photonic engineering of the interferometer sensing and reference waveguides result in sinusoidal TE and TM spectra with substantially different eigen-frequencies. This allows for the instantaneous deconvolution of multiplexed polarizations and enables large spectral shifts and noise reduction through filtering in the Fourier Transform domain. Due to enhanced sensitivity, optical systems can be designed that employ portable spectrum analyzers with nm range resolution without compromising the sensor analytical capability. Practical detection limits in the 10(-6)-10(-7) RIU range are achievable, including temperature effects. Finally, a proof of concept device is realized on a silicon microphotonic chip that monolithically integrates broad-band light sources and single mode silicon nitride waveguides. Refractive index detection limits rivaling that of ring resonators with externally coupled laser sources are demonstrated. Sensitivities of 20 μm/RIU and spectral shifts in the tens of a pm are obtained.

Initial Design and Evaluation of a Pediatric Intra-Cardiac Camera System for Ventricular Septal Defects

The primary objective of this project is to design, fabricate, and test a small, integrated camera system for aiding in the visualization and surgical repair of certain types of ventricular septal defects (VSD), in pediatric patients. Currently, no purpose-designed commercial device to view VSDs from the left ventricle of the heart exists. The left ventricular perspective is ideal for obtaining an unobstructed view of the VSD. This VSD camera device would also provide a platform for passing a suture through the hole in the ventricular septum, with future work implementing additional tools capable of more advanced tasks. This camera device will help solve some of the major issues currently associated with cardiac imaging and surgical closure of VSDs in newborns and young children This paper examines the design development and preliminary evaluation of a proof of concept device. Included are preliminary results of image quality comparisons, design details of a pediatric-specific VSD camera device, and initial outcomes from in vitro testing.

Photochromic Electret: A New Tool for Light Energy Harvesting.

In this paper, a photochromic electret for light energy harvesting is proposed and discussed. Such electret directly converts the photon energy into electric energy thanks to a polarization modulation caused by the photochromic reaction, which leads to a change in dipole moment. Theoretical concepts on which the photochromic electret is based are considered with an estimation of the effectiveness as a function of material properties. Finally, an electret based on a photochromic diarylethene is shown with the photoelectric characterization as a proof of concept device.

Applying Microfluidics to Electrophysiology

Microfluidics can be integrated with standard electrophysiology techniques to allow new experimental modalities. Specifically, the motivation for the microfluidic brain slice device is discussed including how the device docks to standard perfusion chambers and the technique of passive pumping which is used to deliver boluses of neuromodulators to the brain slice. By simplifying the device design, we are able to achieve a practical solution to the current unmet electrophysiology need of applying multiple neuromodulators across multiple regions of the brain slice. This is achieved by substituting the standard coverglass substrate of the perfusion chamber with a thin microfluidic device bonded to the coverglass substrate. This was then attached to the perfusion chamber and small holes connect the open-well of the perfusion chamber to the microfluidic channels buried within the microfluidic substrate. These microfluidic channels are interfaced with ports drilled into the edge of the perfusion chamber to access and deliver stimulants. This project represents how the field of microfluidics is transitioning away from proof-of concept device demonstrations and into practical solutions for unmet experimental and clinical needs.