Transport properties of CuIn1-xAlxSe2/AZnO heterostructure for low cost thin film photovoltaics

CuIn1-xAlxSe2 (CIASe) thin films were grown by a simple sol-gel route followed by annealing under vacuum. Parameters related to the spin-orbit (Delta(SO)) and crystal field (Delta(CF)) were determined using a quasi-cubic model. Highly oriented (002) aluminum doped (2%) ZnO, 100 nm thin films, were co-sputtered for CuIn1-xAlxSe2/AZnO based solar cells. Barrier height and ideality factor varied from 0.63 eV to 0.51 eV and 1.3186 to 2.095 in the dark and under 1.38 A. M 1.5 solar illumination respectively. Current-voltage characteristics carried out at 300 K were confined to a triangle, exhibiting three limiting conduction mechanisms: Ohms law, trap-filled limit curve and SCLC, with 0.2 V being the cross-over voltage, for a quadratic transition from Ohm's to Child's law. Visible photodetection was demonstrated with a CIASe/AZO photodiode configuration. Photocurrent was enhanced by one order from 3 x 10(-3) A in the dark at 1 V to 3 x 10(-2) A upon 1.38 sun illumination. The optimized photodiode exhibits an external quantum efficiency of over 32% to 10% from 350 to 1100 nm at high intensity 17.99 mW cm(-2) solar illumination. High responsivity R-lambda similar to 920 A W-1, sensitivity S similar to 9.0, specific detectivity D* similar to 3 x 10(14) Jones, make CIASe a potential absorber for enhancing the forthcoming technological applications of photodetection.

Enhanced electrochemical performance of graphene nanosheet thin film anode decorated with tin nanoparticles

Graphene nanosheet (GNS) was synthesized by using microwave plasma enhanced CVD on copper substrate and followed by evaporation of tin metal. Scanning and transmission electron microscopy show that nanosize Sn particles are well embedded into the GNS matrix. The composition, structure, and electrochemical properties were characterized by X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), cyclic voltammetry (CV) and chrono-potentiometry. The first discharge capacity of as-deposited and annealed SnGNS obtained was 1551 mA h/g and 975 mA h/g, respectively. The anodes show excellent cyclic performance and coulombic efficiency.

Physics and chemistry of CdTe/CdS thin film heterojunction photovoltaic devices: fundamental and critical aspects

Among the armoury of photovoltaic materials, thin film heterojunction photovoltaics continue to be a promising candidate for solar energy conversion delivering a vast scope in terms of device design and fabrication. Their production does not require expensive semiconductor substrates and high temperature device processing, which allows reduced cost per unit area while maintaining reasonable efficiency. In this regard, superstrate CdTe/CdS solar cells are extensively investigated because of their suitable bandgap alignments, cost effective methods of production at large scales and stability against proton/electron irradiation. The conversion efficiencies in the range of 6-20% are achieved by structuring the device by varying the absorber/window layer thickness, junction activation/annealing steps, with more suitable front/back contacts, preparation techniques, doping with foreign ions, etc. This review focuses on fundamental and critical aspects like: (a) choice of CdS window layer and CdTe absorber layer; (b) drawbacks associated with the device including environmental problems, optical absorption losses and back contact barriers; (c) structural dynamics at CdS-CdTe interface; (d) influence of junction activation process by CdCl2 or HCF2Cl treatment; (e) interface and grain boundary passivation effects; (f) device degradation due to impurity diffusion and stress; (g) fabrication with suitable front and back contacts; (h) chemical processes occurring at various interfaces; (i) strategies and modifications developed to improve their efficiency. The complexity involved in understanding the multiple aspects of tuning the solar cell efficiency is reviewed in detail by considering the individual contribution from each component of the device. It is expected that this review article will enrich the materials aspects of CdTe/CdS devices for solar energy conversion and stimulate further innovative research interest on this intriguing topic.

Sputter Deposited High Capacity Li2-xMnO3-y Films for Thin Film Battery Application

Lithium manganese oxide (Li2-xMnO3-y) thin films have been deposited from activated Li2MnO3 powder by radio frequency magnetron sputtering for the first time in the literature and subjected to electrochemical characterization. Physicochemical characterization by X-ray diffraction has revealed the formation of the thin films with crystallographic phase identical to that of the powder target made of Li2-xMnO3-y. The Li:Mn atomic ratio for the powder and film are calculated by X-ray photoelectron spectroscopy and it is found to be 1.6:1.0. From galvanostatic charge discharge studies, a specific discharge capacity of 139 mu Ah mu m(-1) cm(-2) was obtained when cycled between 2.00 and 3.50 V vs Li/Li+. Additionally the rate capability of the thin film electrodes was studied by subjecting the cells to charge-discharge cycling at different current densities in the range from 10 mu A cm(-2) to 100 mu A cm(-2). (C) 2013 The Electrochemical Society. All rights reserved.

Effect of Heat Pipe Figure of Merit on an Evaporating Thin Film

The performance of a two-phase heat transport device such as the loop heat pipe is influenced by the evaporative heat transfer coefficient in the evaporator. From previous experiments with loop heat pipes, it has been observed that fluids with a high heat pipe figure of merit have a high heat transfer coefficient. Considering an evaporating extended thin film, this paper theoretically corroborates this experimental observation by deriving a direct link between the evaporative heat flux at the interface and the fluid figures of merit (namely interline heat flow parameter and heat pipe figure of merit) in the thin film. Numerical experiments with different working fluids clearly show that a fluid with high figure of merit also has a high cumulative heat transfer in the microregion encompassing the evaporating thin film. Thus, a loop heat pipe or heat pipe that uses a working fluid with a high interline heat flow parameter and heat pipe figure of merit will lead to a high evaporative heat transfer coefficient.

Titanium nitride thin film anode: chemical and microstructural evaluation during electrochemical studies

TIN thin films with (200) fibre texture are deposited on Cu substrate at room temperature using reactive magnetron sputtering. They exhibit a discharge capacity of 172 mu Ah cm(-2) mu m(-1) (300 mAh g(-1)) in a non-aqueous electrolyte containing a Li salt. There is a graded decrease in discharge capacity when cycled between 0.01 and 3.0 V. Electron microscopy investigations indicate significant changes in surface morphology of the cycled TiN electrodes in comparison with the as deposited TiN films. From XPS depth profile analysis, it is inferred that Li intercalated TIN films consist of lithium compounds, hydroxyl groups, titanium sub oxides and TiN. Lithium diffusivity and reactivity decrease with increase in depth and the major reaction with lithium takes place at film surface and grain boundaries. (C) 2014 Elsevier Ltd. All rights reserved.

Epitaxial Co metal thin film grown by pulsed laser deposition using oxide target

We report here the growth of epitaxial Co metal thin film on c-plane sapphire by pulsed laser deposition (RD) using Co:ZnO target utilizing the composition inhomogeneity of the corresponding plasma. Two distinct plasma composition regions have been observed using heavily alloyed Co0.6Zn0.4O target. The central and intense region of the plasma grows Co:ZnO film; the extreme tail grows only Co metal with no trace of either ZnO or Co oxide In between the two extremes, mixed phases (Co +Co-oxides +Co:ZnO) were observed. The Co metal thin film grown in this way shows room temperature ferromagnetism with large in plane magnetization similar to 1288 emu cm(-3) and a coerciviLy of similar to 230 Oe with applied field parallel to the film-substrate interface. Carrier density of the film is similar to 10(22) cm(-3). The film is epiLaxial single phase Co metal which is confirmed by both X-ray diffraction and transmission electron microscopy characierizaLions. Planar Hall Effect (PHE) and Magneto Optic Kerr Effect (MOKE) measurements confirm that the film possesses similar attributes of Co metal. The result shows that the epiLaxial Co metal thin film can be grown from its oxides in the PLD. (C) 2014 Elsevier B.V. All rights reserved.

AIM-Spice Integration of a Recursive Model for Threshold Voltage Shift in Thin Film Transistors

Non-crystalline semiconductor based thin film transistors are the building blocks of large area electronic systems. These devices experience a threshold voltage shift with time due to prolonged gate bias stress. In this paper we integrate a recursive model for threshold voltage shift with the open source BSIM4V4 model of AIM-Spice. This creates a tool for circuit simulation for TFTs. We demonstrate the integrity of the model using several test cases including display driver circuits.

Ultrasonic guided wave sensing properties of PVDF thin film with inter digital electrodes

Ultrasonic strain sensing performance of the large area PVDF with Inter Digital Electrodes (IDE) is studied in this work. Procedure to obtain IDE on a beta-phase PVDF is explained. PVDF film with IDE is bonded on a plate structure and is characterized for its directional sensitivity at different frequencies. Guided waves are induced on the IDE-PVDF sensor from different directions by placing a piezoelectric wafer actuator at different angles. Strain induced on the IDE-PVDF sensor by the guided waves in estimated by using a Laser Doppler Vibrometer (LDV) and a wave propagation model. Using measured voltage response from IDE-PVDF sensor and the strain measurements from LDV the piezoelectric coefficient is estimated in various directions. The variation of 11 e at different angles shows directional sensitivity of the IDE-PVDF sensor to the incident guided waves. The present study provides an effective technique to characterize thin film piezoelectric sensors for ultrasonic strain sensing at very high frequencies of 200 kHz. Often frequency of the guided wave is changed to alter the wavelength to interrogate damages of different sizes in Structural Health Monitoring (SHM) applications. The unique property of directional sensitivity combined with frequency tunability makes the IDE-PVDF sensor most suitable for SHM of structures.

Specroelectrochemical, Switching Kinetics, and Chronoamperometric Studies of Dibenzyl Derivative of Poly(3,4-propylenedioxythiophene) Thin-Film-Based Electrochromic Device

The dibenzyl derivative of poly(3,4-propylenedioxythiophene) (PProDOT-Bz(2)) thin film is deposited onto ITO-coated glass substrate by electropolymerization technique. The electropolymerization of ProDOT-Bz(2) is carried out by a three-electrode electrochemical cell. The cyclic voltammogram shows the redox properties of electrochemically prepared films deposited at different scan rates. The thin films prepared were characterized for its morphological properties to study the homogeniety. Classic six-layer structure of PProDOT-Bz(2) electrochromic device using this material was fabricated and reported for the first and its characterizations such as spectroelectrochemical, switching kinetics, and chronoamperometric studies are performed. The color contrast of the thin film and the device achieved are 64 and 40%, respectively, at lambda(max) (628 nm). The switching time is recorded and the observed values are 5 s from the coloring state to the bleaching state and vice versa. The chronoamperometry shows that the device performed up to 400 cycles, and it is capable of working up to 35 cycles without any degradation. (C) 2014 Wiley Periodicals, Inc.

Influence of curvature on the device physics of thin film transistors on flexible substrates

Thin film transistors (TFTs) on elastomers promise flexible electronics with stretching and bending. Recently, there have been several experimental studies reporting the behavior of TFTs under bending and buckling. In the presence of stress, the insulator capacitance is influenced due to two reasons. The first is the variation in insulator thickness depending on the Poisson ratio and strain. The second is the geometric influence of the curvature of the insulator-semiconductor interface during bending or buckling. This paper models the role of curvature on TFT performance and brings to light an elegant result wherein the TFT characteristics is dependent on the area under the capacitance-distance curve. The paper compares models with simulations and explains several experimental findings reported in literature. (C) 2014 AIP Publishing LLC.

SnO2 nanowire anchored graphene nanosheet matrix for the superior performance of Li-ion thin film battery anode

All solid state batteries are essential candidate for miniaturizing the portable electronics devices. Thin film batteries are constructed by layer by layer deposition of electrode materials by physical vapour deposition method. We propose a promising novel method and unique architecture, in which highly porous graphene sheet embedded with SnO2 nanowire could be employed as the anode electrode in lithium ion thin film battery. The vertically standing graphene flakes were synthesized by microwave plasma CVD and SnO2 nanowires based on a vapour-liquid-solid (VLS) mechanism via thermal evaporation at low synthesis temperature (620 degrees C). The graphene sheet/SnO2 nanowire composite electrode demonstrated stable cycling behaviours and delivered a initial high specific discharge capacity of 1335 mAh g(-1) and 900 mAh g(-1) after the 50th cycle. Furthermore, the SnO2 nanowire electrode displayed superior rate capabilities with various current densities.

Large carbon cluster thin film gauges for measuring aerodynamic heat transfer rates in hypersonic shock tunnels

Different types of Large Carbon Cluster (LCC) layers are synthesized by a single-step pyrolysis technique at various ratios of precursor mixture. The aim is to develop a fast responsive and stable thermal gauge based on a LCC layer which has relatively good electrical conduction in order to use it in the hypersonic flow field. The thermoelectric property of the LCC layer has been studied. It is found that these carbon clusters are sensitive to temperature changes. Therefore suitable thermal gauges were developed for blunt cone bodies and were tested in hypersonic shock tunnels at a flow Mach number of 6.8 to measure aerodynamic heating. The LCC layer of this thermal gauge encounters high shear forces and a hostile environment for test duration in the range of a millisecond. The results are favorable to use large carbon clusters as a better sensor than a conventional platinum thin film gauge in view of fast responsiveness and stability.