Gallium doped ZnO films (GZO) were deposited by reactive co-sputtering of Zn and GaAs at different partial pressures of oxygen in Ar-O2 mixture. The GZO films were deposited at 375 °C, with GaAs area coverage of 0 - 3 % and 4 - 10 % O2 in sputtering atmosphere. The composition of GZO films was studied by X-ray photoelectron spectroscopy, which showed that the films deposited at 4 % and 5 % O2 display Ga/Zn ratio of ∼ 0.1 and contain oxygen vacancies, while those deposited at 6 % and 7 % O2 display Ga/Zn ratio of ∼ 0.01 and contain chemisorbed/interstitial oxygen. X-ray diffraction measurements supported by Raman studies revealed that undoped ZnO films are strongly c-axis oriented and display decrease of crystallite size along c-axis, along with substantial increase of hydrostatic tensile strain with increase of O2 percentage, which are attributed to the presence of interstitial oxygen. In sharp contrast, GZO films deposited at 4 % and 5 % O2 under limited oxygen availability, display smaller and mis-oriented crystallites along c-axis and large compressive strain, which is also hydrostatic, owing to the incorporation of Ga. The GZO films deposited at 6 % and 7 % O2 display improved crystallinity and decrease of compressive strain, which are attributed to reduced Ga content of the films and sufficient availability of oxygen during deposition. This study reveals the critical influence of the partial pressure of oxygen on the stoichiometry, doping concentration, crystallinity and the nature of strain in reactively sputtered GZO films.

Controlling the perovskite film surface is key to improving both the stability and photovoltaic performance of perovskite solar cells. In particular, surface defects on the perovskite films, which are fundamental issues, must be passivated. This work presents a 2D organic material phenyltriethylammonium iodide (PTEAI) to passivate a 3D (FAPbI3)1−x(MAPbBr3)x perovskite film surface. PTEAI forms a well‐matched conformal layer on the perovskite film, protecting the film surface from moisture by preventing the escape of organic ions from the film. The N+ cations and I− anions in PTEAI form bonds with the locally charged perovskite surface, reducing the surface defect density as well as the impeding non‐radiative recombination while enhancing carrier lifetimes. These PTEAI features facilitate significant enhancements in both the open‐circuit voltage (VOC) and fill factor (FF) of the perovskite solar cells. As a result, the champion PTEAI‐based perovskite solar cell exhibits the highest power conversion efficiency of 20.2% compared with 18.8% by the pristine device. Additionally, the PTEAI‐treated device retains 92% of its initial efficiency after being stored in ambient air at room temperature and a relative humidity of 40–60% for 500 h without encapsulation.

The proliferation of advanced analytics and artificial intelligence has been driven by huge volumes of data that are mostly generated at the edge. Simultaneously, there is a rising demand to perform analytics on edge platforms (i.e., near-sensor data analytics). However, conventional architectures of such platforms may not execute the targeted applications in an energy-efficient manner. Emerging near and in-memory computing paradigms can increase the energy efficiency of edge platforms by relying on emerging logic and memory devices. More importantly, these paradigms enable the possibility of performing computations on unconventional platforms, namely flexible computing systems. In this paper, we explore the benefits of in-memory computing at the edge on a flexible substrate enabled by thin-film transistors (TFTs) and resistive RAM (RRAM). As a case study, we consider bio-signal processing application workloads, i.e., compressive sensing and anomaly detection. We model the device, circuit, and architecture of our targeted platform and evaluate the corresponding system-level performance. Preliminary results indicate that in-memory computing enabled by flexible electronic devices enables a new class of edge platforms with lower power consumption, compared to that of rigid TFT devices.

In recent years, the enormous change in landscape of researchers in energy-based research and technologies in the market can be clearly observed. In the recent decades, clean, affordable, and domestic renewable energy and energy harvesters has been one of the key demands addressed towards the robust and diverse electronics applications. To fulfill the need of consumer electronics, plenty of innovative development is in progress in the flexible and stretchable electronics industry, whereas the compatible energy harvesting devices are still lacking the breakthrough for the flexible electronics industry. The renewable energy sector has always been in demand for sustainable and clean resources of energy to save our environment from exhaustive usage of carbon, oils, etc., to keep up with the demand and supply ratio, and to deal with cost factors, since sincere attempts are being made in various energy sectors. Efficient and sustainable renewable energy resources are the current challenge with tedious development for the energy scavenging systems which can capture even nominal power of energy from light, vibration, or thermal sources, etc. With the help of advanced materials and technology, these energy harvesting devices can possibly replace the current energy storage systems like batteries, supercapacitors, hydrogen storage, etc.

Conductive electrodes are major components of flexible optoelectronic devices. However, existing materials are either very conductive but brittle (e.g., ITO [indium tin-oxide]), or non-brittle but less conductive, with an environment-dependent conductivity (e.g., PEDOT:PSS [poly-(3,4 ethylenedioxythiophene): poly (styrene sulfonic acid)]). Here, we propose a new design that simultaneously takes advantage of both the high conductivity of ITO and the high flexibility of PEDOT:PSS. In our design, a PEDOT:PSS interface is inserted between the film substrate and the ITO layer, creating a hybrid layered structure that retains both its high conductivity and high stability, when the film is deformed. The rational behind the creation of this structure, is that PEDOT:PSS, used as an interface between the locally delaminated ITO layer and the substrate, substantially reduces the detrimental effects of cracks on the electrode’s conductivity. These results open the path for a new generation of transparent electrodes in advanced flexible devices.

This article reports on a moldable soft porous composite of liquid metal alloy (LMA) and Ecoflex-0030 elastomer for the first time, where random pores in the composite behaves as tiny triboelectric nanogenerators (TENGs). The triboelectric foam produced a maximum peak-to-peak short-circuit current (I-SC) of similar to 466 nA (charge density = similar to 35 mu C/m(2)) and open circuit voltage (V-OC) of similar to 78 V for a sample of size 5 cm x 5 cm x 1 cm, where the output current is similar to 20% higher than previously reported triboelectric foams based on PDMS and lead zir-conate titanate (PZT)/carbon nanotube (CNT) of equivalent area. In addition, surface texture further increases the foam's softness and enhance the charge generation leading to a 36% increase in triboelectric charge (charge density = similar to 48 mu C/m(2)). A soft monolithic shoe insole is prepared, which produced a range of triboelectric responses in the order of mu A in response to different modes of human motion. Upon jogging, the porous shoe insole with 3 wt parts of LMA in Ecoflex matrix, produce an instantaneous power of similar to 2.6 mW (instantaneous power density = 13 mu W/cm(2)). In addition, the insole also shows capacitive response to deformation, enabling the sensor to perform in-motion force and weight measurement.

Smart skins are integrating an increasing number of functionalities to improve the interactions between the equipped systems (robots or artificial systems) and their ambient environment. Here, we introduce a controllable texture as a new functionality, based on an innovative soft technology that leverages the strong electro-mechanical coupling of our all-polymer design, which can be easily embedded to a wide range of systems. The device comprises a polymer-based heating element [doped PEDOT:PSS (poly-(3,4 ethylenedioxythiophene): poly (styrene sulfonic acid))], a polymer-based soft actuator (Ecoflex 00–50/ethanol) and a polymer-based casing [PDMS (polydimethylsiloxane)]. We introduce a smart pipe prototype module and use our controllable polymorph skin to tailor the interaction between the pipe and the fluid. This allows us to obtain a 50% reduction of the friction coefficient in turbulent regime, between non-actuated and actuated configurations. This concept may find applications in engineering fields such as smart skin-based touch control and controllable friction coefficients.

Thermoelectric generators (TEGs) are interesting energy harvesters of otherwise wasted heat. Here, a polymer‐assisted generic process and its mechanics to obtain sputtered thermoelectric (TE) telluride material‐based 3D tubular structures with unprecedented length (up to seamless 4 cm and further expandable) are shown. This length allows for large temperature differences between the hot and the cold ends, a critical but untapped enabler for high power generation. Compared with a flat slab, better area efficiency is observed for a rolled tube and compared with a solid rod architecture, a rolled tube uses less material (thus making it lightweight and cost effective) and has competitive performance advantage due to a smaller contact area. It is also shown that a tubular architecture thermopile‐based TEG is able to generate up to 5 μW of power (eight pairs of p‐ and n‐type thermopiles) through a temperature difference of 60 °C. The demonstrated process can play an important role in transforming 2D atomic crystal structure TE materials into 3D tubular thermopiles for effective TEG application, which can maintain higher temperature differences by longer distances between hot and cold ends.

As we are at the verge of entering the era of Internet-of-Things (IoT), there is a clear need to produce continuous power supply to the huge amount of electronic devices that must be wirelessly interconnected and operate uninterruptedly. At the same time, new mechanical constrains arise from the fact that these devices should be ubiquitous, which leads to the need of lightweight and mechanical compliance to any shape or surface. As an important renewable energy source, a mechanically adaptable thermoelectric generator (TEG) can make use of the usually wasted thermal differences between ambient and technology-users to power-up such systems. With this idea in mind, we have developed a simple approach to fabricate TEGs, based on commonly available substrates (paper or polymers) and assisted through simple folding and cutting techniques (born from origami and kirigami) to form strategic structures (serpentine, helical, spiral, etc.) with the mechanical advantage of foldability and over 100% demonstrated stretchability. The use of these methods and structures allows the mechanical reconfigurability of the devices to, for example, increase the temperature difference in a TEG, thus its power, or allow a more efficient use of area and therefore increase the power density. We will discuss the strategies to effectively integrate folding and cutting techniques with common materials and the basic TEG configuration, as well as demonstrate the devices’ implementation and characterization. Finally, we believe our simple integration approach offers an interesting and versatile methodology, which can be easily extrapolated to new materials and technologies for a greater variety of applications.

Nature-inspired structures as transparent conducting electrodes are exciting alternatives to conventional TCEs because they provide higher transmittance and conductivity at low temperatures on flexible substrates. The current work is focussed to develop a metal mesh structure with the help of plant leaf vein as a template. Bilayer metal mesh of thickness < 100 nm was deposited and transferred to flexible plastic substrate at room temperature. Scanning electron microscopy images were used to obtain the ratio of open area space and covered space of the electrodes. The bilayer metal mesh structure shows high optical transmittance (>85%) and electrical resistivity of the order of 10(-4) Omega cm. The metal mesh TCE based on leaf vein template opens up new ways of obtaining large charge transfer resolving the junction resistance problem encountered in case of metal nanowires. (C) 2018 Elsevier B.V. All rights reserved.

In article number 1700192, a tubular architecture of thermoelectric generator modules is introduced by Muhammad M. Hussain and co-workers. A polymer-assisted generic process and its mechanics to obtain sputtered thermoelectric (TE) telluride materials based 3D tubular structures with unprecedented length (up to seamless 4 cm and further expandable) are shown.

Thermoelectric generators are interesting energy harvesting option due to its clean nature, silent operation and it harnesses the power from otherwise wasted heat. While most of the research has been directed toward high thermoelectric performance based material innovation, we have focused on its architecture and how to connect hot and cold ends when they are far apart. From that perspective, we have devised an effective integration strategy to roll-up otherwise ultra-thin layers of thermoelectric materials to form tubular architecture and to integrate them in array for high power thermoelectric generator development. We have used widely used thermoelectric materials such as bismuth telluride (Bi2Te3) and antimony telluride (Sb2Te3). We also offer an analytical methodology to deduce the effective mechanics of the strain associated with the thermoelectric materials and the used polymeric materials (as stressor and as support layers). Experimentally we have shown seamless 4 cm (and further expandable) tubular arrays of thermoelectric piles. Such a long length allows us to connect to far apart hot and cold end for higher power generation as we also maintain higher temperature difference for longer time. We also compare its effectiveness with solid slab and wire of the same tube from its performance and cost perspective. At the initial stage we report up to 5 μW (8 pairs of p and n-type thermopiles) through a temperature difference of 60 °C. We also show how this can be improved further and potential integration strategy with 2D material system.

As we are advancing our world to smart living, a critical challenge is increasingly pressing - increased energy demand. While we need mega power supplies for running data centers and other emerging applications, we also need instant small- scale power supply for trillions of electronics that we are using and will use in the age of Internet of Things (IoT) and Internet of Everything (IoE). Such power supplies must meet some parallel demands: sufficient energy supply in reliable, safe and affordable manner. In that regard, thermoelectric generators emerge as important renewable energy source with great potential to take advantage of the widely-abundant and normally-wasted thermal energy. Thanks to the advancements of nano-engineered materials, thermoelectric generators' (TEG) performance and feasibility are gradually improving. However, still innovative engineering solutions are scarce to sufficiently take the TEG performance and functionalities beyond the status-quo. Opportunities exist to integrate them with emerging fields and technologies such as wearable electronics, bio-integrated systems, cybernetics and others. This review will mainly focus on unorthodox but effective engineering solutions to notch up the overall performance of TEGs and broadening their application base. First, nanotechnology's influence in TEGs' development will be introduced, followed by a discussion on how the introduction of mechanically reconfigurable devices can shape up the emerging spectrum of novel TEG technologies. (C) The Author(s) 2017. Published by ECS.

Multilayer thin films of SnO2/Ag/SnO2 were prepared on silicon and quartz substrates by electron beam and thermal evaporation method for the SnO2 and Ag layer respectively. As prepared specimen were irradiated with 120 MeV Ni7+ ions of two fluences of 1x10(12) and 5x10(12) ions /cm(2) to modify the structural and optical properties. These films were then systematically investigated to observe the modifications produced in the multilayer films. XRD was used for structural investigation which shows crystallinity induced by irradiation in the otherwise amorphous samples. FTIR results reveal the presence of functional groups with stretching and bending vibration. The average transmittance of the pristine multilayer film was similar to 73% which shows a slight increase on irradiation. Peak positions in Raman spectra are indicative of strain in the irradiated sample. A decrease in grain size is observed after irradiation.

Thermoelectricity can be an interesting source of power from otherwise wasted heat. Therefore, for many decades discovery and optimization of new thermoelectric materials has shown important leap toward thermoelectric generator applications. However, from an engineering perspective, structural modifications at the device level can play an important role to maximize the power output. We base our study on device architecture reconfiguration by adopting various in-plane and out-of-plane fractal design to develop flexible and stretchable thermoelectric generator. Physical flexibility allows the devices to be conforming to asymmetric surfaces and mechanical stretching allows to dynamically controlling the distance between the hot and cold end in a thermoelectric generator. This way, one can tune the distance, maximize the temperature difference and maintain a high temperature difference which directly relates to efficiency of a thermoelectric generator. Adopting low cost materials like paper and Off-Stoichiometry Thiol-Enes (OSTE) as structural materials we demonstrate the integration strategy to rationally design materials, processes and devices for flexible and stretchable thermoelectric generators.

Paper has been an essential material in our daily life since ancient times. Its affordability, accessibility, adaptability, workability and its easiness of usage makes it an attractive structural material to develop many kind of technologies such as flexible electronics, and energy storage and harvesting devices. Additionally, the scientific community has increased its interest on waste heat as an environmentally friendly energy source to support the increasing energy demand. Therefore, in this paper we described two affordable and flexible thermoelectric nanogenerators (TEGs) developed on paper substrates by the usage of simple micromachining and microfabrication techniques. Moreover, they exhibit mechanical stability and adaptability (through folding and cutting techniques) for a diverse set of scenarios where vertical or horizontal schemes can be conveniently used depending on the final application. The first TEG device, implemented on standard paper, generated a power of 0.5nW (ΔT=50K). By changing the substrate to a tearless and extra-smooth polyester paper, the TEG performance was optimized achieving less internal resistance and a greater power of ~80nW (ΔT=75K), at the cost of more rigidity in the substrate. This power represented over three times higher power production than the standard paper–based TEG with same dimensions, number of thermoelectric pairs and temperature difference. Another interesting aspect of paper based TEG is due to its foldability, one can control the temperature difference by unfolding (larger separation between hot and cold ends) and folding (smaller separation). Finally, one of the underlying objectives of this work is to spread the availability of essential technologies to the broad population by inclusion of everyday materials and simple processes.

To achieve higher power output from a thermoelectric generator (TEG), one needs to maintain a larger temperature difference between hot and cold end. In that regard, a stretchable TEG can be interesting to adaptively control the temperature difference. Here we show, the development of simple yet versatile and highly stretchable thermoelectric generators (TEGs), by combining well-known inorganic thermoelectric materials Bismuth Telluride and Antimony Telluride (Bi2Te3 and Sb2Te3) with organic substrates (Off-Stoichiometry Thiol-Enes polymer platform – OSTE, polyimide or paper) and novel helical architecture (double-arm spiral/helix) to achieve over 100% stretchability. First, an OSTE-based TEG design demonstrates higher open circuit voltage generation at 100% strain than at rest, although it exhibits high internal resistance and a relatively complex fabrication process. The second, simpler TEG design, achieves a significant resistance reduction and two different structural substrates (PI and paper) are compared. The paper-based TEG generates 17nW (ΔT=75°C) at 60% strain, which represents more than twice the power generation while at rest (zero strain). On the other hand, polyimide produces more conductive TE films and higher power (~35nW at ΔT=75°C) but due to its higher thermal conductivity, power does not increase at stretch. In conclusion, highly stretchable TEGs can lead to higher temperature gradients (thus higher power generation), given that thermal conductivity of the structural material is low enough. Furthermore, either horizontal or vertical displacement can be achieved with double-arm helical architecture, hence allowing to extend the device to any nearby and mobile heat sink for continuous, effectively higher power generation.

Epitaxial GaN films were grown on sputtered ZnO buffer layers of thickness 25–200 nm over c-plane sapphire by reactive sputtering of GaAs in nitrogen at 700 °C. The epitaxial quality and microstructure have been studied by high resolution X-ray diffraction in phi (ϕ) and omega (ω) scan geometries. The surface morphology of epilayers was studied by atomic force microscopy and scanning electron microscopy and their crystalline quality was assessed by Raman spectroscopy. These studies have shown that ZnO buffer layers of 50–100 nm facilitate growth of GaN epilayers of high crystalline quality, compared to those grown on thinner and thicker ZnO buffer layers.

In this paper, we present the impact of swift heavy ion beam irradiation on the structural, optical and electronic properties of SnO2 thin films. Thin films were deposited using the pulsed laser deposition technique on Al2O3 substrates. Atomic force microscopy, X-ray diffraction, UV-visible absorption and temperature-dependent resistivity measurements were performed to explore the morphological, structural, optical and electronic properties of the as-deposited and irradiated samples. The peak intensity of the (200) peak was found to decrease monotonously with increasing irradiation fluence. The band gap energy of the 1x1011ion/cm2 irradiated sample was found to increase. The electrical resistivity of the samples showed a continuous increase with the irradiation fluence.