Electroplating of CdTe thin films from cadmium sulphate precursor and comparison of layers grown by 3-electrode and 2-electrode systems

Electrodeposition of CdTe thin films was carried out from the late 1970s using the cadmium sulphate precursor. The solar energy group at Sheffield Hallam University has carried out a comprehensive study of CdTe thin films electroplated using cadmium sulfate, cadmium nitrate and cadmium chloride precursors, in order to select the best electrolyte. Some of these results have been published elsewhere, and this manuscript presents the summary of the results obtained on CdTe layers grown from cadmium sulphate precursor. In addition, this research program has been exploring the ways of eliminating the reference electrode, since this is a possible source of detrimental impurities, such as K+ and Ag+ for CdS/CdTe solar cells. This paper compares the results obtained from CdTe layers grown by three-electrode (3E) and two-electrode (2E) systems for their material properties and performance in CdS/CdTe devices. Thin films were characterized using a wide range of analytical techniques for their structural, morphological, optical and electrical properties. These layers have also been used in device structures; glass/FTO/CdS/CdTe/Au and CdTe from both methods have produced solar cells to date with efficiencies in the region of 5%–13%. Comprehensive work carried out to date produced comparable and superior devices fabricated from materials grown using 2E system

Polymer Nanocomposite Thin Film Mirror for the Infrared Region**

Thin film metal oxide coatings have been used commercially as electromagnetic filters from the UV to infrared regions for over half a century. Deposition onto a substrate has typically been accomplished using vapor deposition techniques [10] This paper describes the first time demonstration of an IR mirror using a relatively inexpensive method to apply complicated thin film dielectric stacks to a polymer substrate that can function effectively in high strain systems. Ultrathin layers of polymer nanocomposites can be used to develop electromagnetic filters, with improved mechanical performance, on compliant substrates such as polymers. Self-assembled polymer nanocomposite thin film layers composed of UV-cured acrylates and metal oxide nanoparticles were developed as antireflective coatings for ophthalmic lenses. Anti-reflective coatings for the visible range are relatively simple designs of several dielectric layers and are used in many consumer products. These same materials can also be used to create mirrors in the IR region, but the layer counts increases to tens of layers resulting in more complexity in the process. For processes involving dielectric materials, these increased interfaces increase the vulnerability of the coatings to cracking when it is applied to a flexible substrate. A simple thin film filter design utilizes a stack of ¼ wave thickness layers of alternating high and low refractive index materials for which the reflection off a surface is given by Equation 1. where R is reflection, n 0 is index of refraction of air, and Y is admittance of the surface. [13] The admittance of a reflective stack of i alternating ¼ wave high and low refractive index layers is expressed in Equation 2. This simple relationship allows the determination of the filter response at a specified wavelength (l) having layer thicknesses equal to 0.25 l/d (d is the optical thickness, which is the product of the refractive index and thickness of the film). The nanocomposite thin films will require more layers than those produced by vacuum deposition since the ratio of refractive indices is less because of the organic binder used in this system. Reproducible optical response of multilayer filters is only accomplished through precise control of the refractive index and thickness of each layer. In general, preferred layer characteristics include uniform thickness over surface contours, low surface roughness relative to its thickness for sharp differences in refractive index across the layer interfaces, and the highest possible difference in refractive index between adjacent layers maximizing the admittance of the surface. The nanocomposite thin films consist of essentially spherical metal oxide nanoparticles with narrow size distributions dispersed in a continuous matrix of UV-cured acrylate polymer. High transparency and low scattering for each layer require that the nanoparticles are not agglomerated and are significantly smaller in diameter than the waves to be altered. The functional materials and processes described here have allowed our group to achieve the necessary volume densities of nanoparticles without agglomerations. The packing of the nanoparticles was pushed toward to the theoretical limit of 73% for hexagonal close packing of spheres in order to generate the largest possible refractive index difference between layers. For our set of processing conditions and materials, volume packing of 60% yielded highly reproducible mechanical performanc

Ultrafast charge carrier relaxation and charge transfer processes in CdS/CdTe thin films

Ultrafast transient absorption pump–probe spectroscopy (TAPPS) has been employed to investigate charge carrier relaxation in cadmium sulfide/cadmium telluride (CdS/CdTe) nanoparticle (NP)-based thin films and electron transfer (ET) processes between CdTe and CdS. Effects of post-growth annealing treatments to ET processes have been investigated by carrying out TAPPS experiments on three CdS/CdTe samples: as deposited, heat treated, and CdCl2 treated. Clear evidence of ET process in the treated thin films has been observed by comparing transient absorption (TA) spectra of CdS/CdTe thin films to those of CdS and CdTe. Quantitative comparison between ultrafast kinetics at different probe wavelengths unravels the ET processes and enables determination of its rate constants. Implication of the photoinduced dynamics to photovoltaic devices is discussed

Room Temperature Synthesis of a Copper Ink for the Intense Pulsed Light Sintering of Conductive Copper Films

Conducting films are becoming increasingly important for the printed electronics industry with applications in various technologies including antennas, RFID tags, photovoltaics, flexible electronics, and displays. To date, expensive noble metals have been utilized in these conductive films, which ultimately increases the cost. In the present work, more economically viable copper based conducting films have been developed for both glass and flexible PET substrates, using copper and copper oxide nanoparticles. The copper nanoparticles (with copper­(I) oxide impurity) are synthesized by using a simple copper reduction method in the presence of Tergitol as a capping agent. Various factors such as solvent, pH, and reductant concentration have been explored in detail and optimized in order to produce a nanoparticle ink at room temperature. Second, the ink obtained at room temperature was used to fabricate conducting films by intense pulse light sintering of the deposited films. These conducting films had sheet resistances as low as 0.12 Ω/□ over areas up to 10 cm² with a thickness of 8 μm

Fabrication of Elemental Copper by Intense Pulsed Light Processing of a Copper Nitrate Hydroxide Ink

Printed electronics and renewable energy technologies have shown a growing demand for scalable copper and copper precursor inks. An alternative copper precursor ink of copper nitrate hydroxide, Cu₂(OH)₃NO₃, was aqueously synthesized under ambient conditions with copper nitrate and potassium hydroxide reagents. Films were deposited by screen-printing and subsequently processed with intense pulsed light. The Cu₂(OH)₃NO₃ quickly transformed in less than 100 s using 40 (2 ms, 12.8 J cm^–2) pulses into CuO. At higher energy densities, the sintering improved the bulk film quality. The direct formation of Cu from the Cu₂(OH)₃NO₃ requires a reducing agent; therefore, fructose and glucose were added to the inks. Rather than oxidizing, the thermal decomposition of the sugars led to a reducing environment and direct conversion of the films into elemental copper. The chemical and physical transformations were studied with XRD, SEM, FTIR and UV–vis

Ultrafast Carbon Dioxide Sorption Kinetics Using Lithium Silicate Nanowires

In this paper, the Li₄SiO₄ nanowires (NWs) were shown to be promising for CO₂ capture with ultrafast kinetics. Specifically, the nanowire powders exhibited an uptake of 0.35 g g^–1 of CO₂ at an ultrafast adsorption rate of 0.22 g g^–1 min^–1 at 650–700 °C. Lithium silicate (Li₄SiO₄) nanowires and nanopowders were synthesized using a “solvo-plasma” technique involving plasma oxidation of silicon precursors mixed with lithium hydroxide. The kinetic parameter values (<i>k</i>) extracted from sorption kinetics obtained using NW powders are 1 order of magnitude higher than those previously reported for the Li₄SiO₄–CO₂ reaction system. The time scales for CO₂ sorption using nanowires are approximately 3 min and two orders magnitude faster compared to those obtained using lithium silicate powders with spherical morphologies and aggregates. Furthermore, Li₄SiO₄ nanowire powders showed reversibility through sorption–desorption cycles indicating their suitability for CO₂ capture applications. All of the morphologies of Li₄SiO₄ powders exhibited a double exponential behavior in the adsorption kinetics indicating two distinct time constants for kinetic and the mass transfer limited regimes

Mn-Rich NMC Cathode for Lithium-Ion Batteries at High-Voltage Operation

Development in high-rate electrode materials capable of storing vast amounts of charge in a short duration to decrease charging time and increase power in lithium-ion batteries is an important challenge to address. Here, we introduce a synthesis strategy with a series of composition-controlled NMC cathodes, including LiNi0.2Mn0.6Co0.2O2(NMC262), LiNi0.3Mn0.5Co0.2O2(NMC352), and LiNi0.4Mn0.4Co0.2O2(NMC442). A very high-rate performance was achieved for Mn-rich LiNi0.2Mn0.6Co0.2O2 (NMC262). It has a very high initial discharge capacity of 285 mAh g−1 when charged to 4.7 V at a current of 20 mA g−1 and retains the capacity of 201 mAh g−1 after 100 cycles. It also exhibits an excellent rate capability of 138, and 114 mAh g−1 even at rates of 10 and 15 C (1 C = 240 mA g−1). The high discharge capacities and excellent rate capabilities of Mn-rich LiNi0.2Mn0.6Co0.2O2 cathodes could be ascribed to their structural stability, controlled particle size, high surface area, and suppressed phase transformation from layered to spinel phases, due to low cation mixing and the higher oxidation state of manganese. The cathodic and anodic diffusion coefficient of the NMC262 electrode was determined to be around 4.76 × 10−10 cm2 s−1 and 2.1 × 10−10 cm2 s−1, respectively

Intense pulsed light treatment of cadmium telluride nanoparticle-based thin films

The search for low-cost growth techniques and processing methods for semiconductor thin films continues to be a growing area of research; particularly in photovoltaics. In this study, electrochemical deposition was used to grow CdTe nanoparticulate based thin films on conducting glass substrates. After material characterization, the films were thermally sintered using a rapid thermal annealing technique called intense pulsed light (IPL). IPL is an ultrafast technique which can reduce thermal processing times down to a few minutes, thereby cutting production times and increasing throughput. The pulses of light create localized heating lasting less than 1 ms, allowing films to be processed under atmospheric conditions,avoiding the need for inert or vacuum environments. For the first time, we report the use of IPL treatment on CdTe thin films. X-ray diffraction (XRD), optical absorption spectroscopy (UV−Vis), scanning electron microscopy (SEM) and room temperature photoluminescence (PL) were used to study the effects of the IPL processing parameters on the CdTe films. The results found that optimum recrystallization and a decrease in defects occurred when pulses of light with an energy density of 21.6 J cm−2 were applied. SEM images also show a unique feature of IPL treatment: the formation of a continuous melted layer of CdTe, removing holes and voids from a nanoparticle-based thin film