CdTe

Recent progress with indium (III) sulfide (In2S3)-buffered thin film solar cells (TFSC) was briefly reviewed. In2S3 has emerged as a promising low-hazard buffer (or window) material, and has proven to improve the properties of the solar cells, while reducing toxicity. Various deposition techniques have been employed to synthesize In2S3 films on different types of substrates.  Until now, atomic layer deposition (ALD) and ionic layer gas atomic reaction (ILGAR) techniques have been the two most successful, yielding maximum energy conversion efficiencies up to 16.4% and 16.1%, respectively. The impact of varied deposition parameters upon the In2S3 film properties and performance of cadmium (Cd)-free solar cells has been outlined. A comparative/operational analysis (solar cell efficiencies above 9% reported for cell area ≤ 1cm2) of various buffer layers used in two primary types of TFSC technology: chalcopyrite (CIS/CIGS)- and CdTe-based solar cells was also performed to measure the progress of In2S3 compared to its counterparts.

We report on a characterization study of a multi-row direct-conversion x-ray detector used to generate the first photon counting clinical x-ray computed tomography (CT) patent images. In order to provide the photon counting detector with adequate performance for low-dose CT applications, we have designed and fabricated a fast application specific integrated circuit (ASIC) for data readout from the pixellated CdTe detectors that comprise the photon counting detector. The cadmium telluride (CdTe) detector has 512 pixels with a 1 mm pitch and is vertically integrated with the ASIC readout so it can be tiled in two dimensions similar to those that are tiled in an arc found in 32-row multi-slice CT systems. We have measured several important detector parameters including the maximum output count rate, energy resolution, and noise performance. Additionally the relationship between the output and input rate has been found to fit a non-paralyzable detector model with a dead time of 160 nsec. A maximum output rate of 6 × 106 counts per second per pixel has been obtained with a low output x-ray tube for CT operated between 0.01 mA and 6 mA at 140 keV and different source-to-detector distances. All detector noise counts are less that 20 keV which is sufficiently low for clinical CT. The energy resolution measured with the 60 keV photons from a 241Am source is ~12%. In conclusion, our results demonstrate the potential for the application of the CdTe based photon counting detector to clinical CT systems. Our future plans include further performance improvement by incorporating drift structures to each detector pixel.

The exceptional properties of localised surface plasmons (LSPs), such as local field enhancement and confinement effects, resonant behavior, make them ideal candidates to control the emission of luminescent nanoparticles. In the present work, we investigated the LSP effect on the steady-state and time-resolved emission properties of quantum dots (QDs) by organizing the dots into self-assembled dendrite structures deposited on plasmonic nanostructures. Self-assembled structures consisting of water-soluble CdTe mono-size QDs, were developed on the surface of co-sputtered TiO2 thin films doped with Au nanoparticles (NPs) annealed at different temperatures. Their steady-state fluorescence properties were probed by scanning the spatially resolved emission spectra and the energy transfer processes were investigated by the fluorescence lifetime imaging (FLIM) microscopy. Our results indicate that a resonant coupling between excitons confined in QDs and LSPs in Au NPs located beneath the self-assembled structure indeed takes place and results in (i) a shift of the ground state luminescence towards higher energies and onset of emission from excited states in QDs, and (ii) a decrease of the ground state exciton lifetime (fluorescence quenching).

CdTe/CdS poly-crystalline thin film solar cells are characterized by means of dark current-voltage (I-V) and capacitance-voltage (C-V) measurements, both as a function of temperature. The studied CdTe/CdS solar cells were fabricated using a novel gaseous thermal treatment in the presence of chloride. I-V curves analysis allows us to extract information about carrier transport phenomena as a function of temperature. From C-V curves we can obtain the doping profiles and analyze the traps levels distribution in the absorber material.

The Rutherford Appleton Laboratory has built a small pixel detector for spectroscopic measurements of high energy X-rays using CdTe and CdZnTe. The detector has an array of 20×20 pixels on a 250μm pitch with each pixel bonded to a separate channel on an application specific integrated circuit (ASIC). Each channel in the ASIC contains a charge preamplifier, leakage current compensation circuit, shaping amplifier and peak hold circuit. In recent years there has been an increase in the availability of high quality CdTe and CdZnTe material and the contacting technology required for low leakage current small pixel devices. The energy resolution and stability of the X-ray performance of 1mm thick CdTe with Aluminum Schottky contact pixels and 2mm thick CdZnTe grown by travelling heater method (THM) are measured. The CdTe detectors had an energy resolution of 1 to 1.1keV at 75keV. The THM CdZnTe had an energy resolution of 1.3keV at 75keV. The stability of the performance was measured over a 12 hour exposure with the detectors biased to -500V and held at 25°C. The CdZnTe exhibited stable performance whereas the CdTe suffered from bias induced polarization, the onset of which was delayed by cooling the detectors to 12°C.

The most commonly used commercial conducting glass is the coated SnO2:F glass substrate. However, it usually presents poor morphological properties and therefore is not adequate for solar cell applications. In this work, we report results about the morphological properties improvement of commercial conductive glass by the deposition of a SnO2 buffer layer by spray pyrolysis technique. The use of a high
resistivity transparent layer (buffer) onto low resistivity transparent oxide has been found to improve the solar cell performance. The methodology for improving film morphology through the deposition of SnO2 buffer layers by spray pyrolysis technique, with appropriate electro-optical properties, is presented. The solar cell results related to the use of an automatized spray pyrolysis system are presented.

This paper presents a 1μm×1.25μm×1µm heterojunction thin film photovoltaic cell having "p-i1-i2-n" cell structure. The designed "ITO/p-CdTe/i1-CdTe/i2-a-Si/n-a-Si/ITO" photovoltaic cell is investigated, optimized and simulated in Silvaco TCAD. Finite Element Analysis (FEA) has been carried out to cater all physical and numerical models to generate practical results. For improvement in cell efficiency, a 1.52 eV wide-bandgap player of CdTe is used which specifically improves the short circuit current (JSC). JSC is directly involved in the improvement of conversion efficiency. For the active region, an intrinsic CdTe layer is combined with an intrinsic amorphous silicon (a-Si) layer. This combination of intrinsic layers in active region is responsible for maximum absorption of photons with a wide range of energies and results in additional electron hole pair generation. Selective absorption is used to maximize light trapping and strong scattering of incident light into active region. Indium Tin Oxide (ITO) is used as front layer and back contact layer with Aluminum (Al) because it offers low resistivity of ~10-4 Ωcm and a transmittance of greater than 90%. Results have been validated by implementing two reported cells with p-ii-n and p-in structures. The results indicate achievement of 28.05% conversion efficiency of the proposed heterojunction cell. The achieved efficiency is better than the efficiencies of the related cells compared in this work and also higher than that of the 25.6% of conventional Heterojunction Intrinsic Thin-film (HIT) silicon solar cells.

In this study, we developed a selective and sensitive inner filter effect-based method by thioglycolic acid capping CdTe quantum dots (TGA-CdTe QDs) for the quantitative determination of Vitamin B12 (B12). The effect of all experimental parameters and possible interference agents for determination of B12 by TGA-CdTe, were individually investigated and optimized. In addition, the mechanism of this detection method was discussed in detailed. Under the optimum conditions, the fluorescence-quenching rate of the TGA-CdTe QDs showed a relative linear relationship against B12 concentration in the ranges of 0.02-0.4 and 1.5-70.0 µM B12 with a detection limit of 2.0×10-8 M. Furthermore, the accuracy, precision and the practical application of determination of B12 by this developed method, were studied in pharmaceutical formulations injection without any sample pretreatment process. The percentage recoveries for B12 determination in these real samples were obtained in the range of 95.0%-105.0%.

In very-high-spatial-resolution gamma-ray imaging applications, such as preclinical PET and SPECT, estimation of 3D interaction location inside the detector crystal can be used to minimize parallax error in the imaging system. In this work, we investigate the effect of bias voltage setting on depth-of-interaction (DOI) estimates for a semiconductor detector with a double-sided strip geometry. We first examine the statistical properties of the signals and develop expressions for likelihoods for given gamma-ray interaction positions. We use Fisher Information to quantify how well (in terms of variance) the measured signals can be used for DOI estimation with different bias-voltage settings. We performed measurements of detector response versus 3D position as a function of applied bias voltage by scanning with highly collimated synchrotron radiation at the Advanced Photon Source at Argonne National Laboratory. Experimental and theoretical results show that the optimum bias setting depe...

We have studied the Raman and luminescence spectra of a microcavity–quantum dot system consisting of a melamine formaldehyde latex microsphere coated by CdTe colloidal quantum dots. The cavity-induced enhancement of the Raman scattering allows the observation of Raman spectra from only a monolayer of CdTe quantum dots. Periodic structure with very narrow peaks in the luminescence spectra of a single microsphere was detected arising from the coupling between the emission from quantum dots and spherical cavity modes. Strong anti-Stokes emission from CdTe quantum dots coupled to the cavity modes was observed using low intensity below band-gap excitation and attributed to the strong field enhancement at the microcavity resonances.

The concentrations of defects forming at near-midgap level in high-resistivity CdTe were estimated on the basis of room-temperature lux-ampere characteristics. A simple model explaining their sublinear dependence based on the presence of discrete levels near the midgap is presented. It is shown that accumulation of space charge in the sample can explain the observed experimental data. Theoretical calculations show that

The CdTe/Si solar cells have been fabricated on p-Si wafer by thermal evaporation method at different thicknesses of n-CdTe (100, 300, 500, and 700nm). The structural and electrical properties including x-ray diffraction, AFM analysis and I-V characteristics are studied and interpreted. For the back and front contacts, gold and indium tin oxide (ITO) are used respectively. Choosing gold as a good back contact is because of its suitable work function with respect to electron affinity and energy gap of silicon. While ITO is chosen as a good front contact for its special properties of good conductivity and transparency. XRD patterns show a good crystallinity of CdTe films and AFM images show a good smoothness of the surface topography of these films. From Hall Effect measurements, we found that the mobilityof charge carriers is 820cm 2 /V-s. From the I-V curves, we found that the quantum efficiency and fill factor have maximum values at the thickness of 500nm (η=3.61%, and FF=0.39).In ...

ABSTRACT This review highlights recent developments in the grafting of conjugated polymers onto various substrates for organic electronic devices. The rapid development of multi-layer architectures demands the preparation of well-defined interfaces between both compatible and incompatible materials. It is promising therefore that interface-engineering is now known to help passivate charge trap states, control energy level alignments, enhance charge extraction, guide active-layer morphologies, and improve material compatibility, adhesion and device stability. In organic electronic devices, conjugated polymers are in contact with a wide range of constituents, such as metals, metal oxides, organic materials, and inorganic particles. Covalent bonds between these materials and macromolecules are desired to yield intimate contacts and well-defined interfaces. Following an overview of the various synthetic methodologies of conjugated polymers, the chemistry of tethering macromolecular chains onto nanoparticles and flat surfaces is described. The creation of functional hybrid materials offers the potential to deliver efficient and low-cost devices.

AlGaAs structures with different aluminum concentration (x=0.0, 0.17, 0.30, and 0.40) were characterized by photoluminescence and photoreflectance techniques. The temperature dependence of optical transitions in the temperature ranging from 2 to 300 K were investigated. Y. P. Varshni [Physica (Utrecht) 34, 194 (1967)], L. Vin~a et al. [Phys. Rev. B 30, 1979 (1984)], and R. Pässler [Phys. Status Solidi B 200, 155 (1997)] models were used to fit the experimental points. The Pässler model gave the best adjustment to the experimental points. The tree models showed that the empirical parameters obtained through the adjustment of the experimental data in the three different models are aluminum composition dependent in the ternary alloy.