15 research outputs found
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%ā13%. 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 Ā¼ 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 Ā¼ 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 pumpāprobe 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 copperĀ(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 Ī©/ā” over areas
up to 10 cm<sup>2</sup> with a thickness of 8 Ī¼m
Scalable Solution Processing of Cu:NiO<sub><i>x</i></sub> Nanoparticles for Perovskite Solar Cells
Transitioning perovskite solar cells from a small-scale
spin coating
to industrial processed slot die coatings requires the development
of scalable charge transport layers. Metal oxide nanoparticles are
strong contenders for these materials, but solvent systems in which
they are stable and can be deposited effectively are required. In
this study, stable copper-doped nickel oxide dispersions in waterāalcohol
were developed using Hansen solubility parameters. The resulting inks
are compatible with blade coating and slot die roll-to-roll processes.
Intense pulsed light (IPL) annealing was applied to further decrease
the processing time and improve device performance. The champion blade-coated
device, with IPL annealing, had a power conversion efficiency (PCE)
of 12.58%. The results were reproduced using roll-to-roll processing
with IPL, yielding a champion device PCE of 12.23% when finished with
C60
Fabrication of Elemental Copper by Intense Pulsed Light Processing of a Copper Nitrate Hydroxide Ink
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, Cu<sub>2</sub>(OH)<sub>3</sub>NO<sub>3</sub>, 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 Cu<sub>2</sub>(OH)<sub>3</sub>NO<sub>3</sub> quickly transformed in less than 100 s using 40 (2
ms, 12.8 J cm<sup>ā2</sup>) pulses into CuO. At higher energy
densities, the sintering improved the bulk film quality. The direct
formation of Cu from the Cu<sub>2</sub>(OH)<sub>3</sub>NO<sub>3</sub> 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 UVāvis
Stable and Flexible Sulfide Composite Electrolyte for High-Performance Solid-State Lithium Batteries
Ultrafast Carbon Dioxide Sorption Kinetics Using Lithium Silicate Nanowires
In this paper, the Li<sub>4</sub>SiO<sub>4</sub> nanowires (NWs)
were shown to be promising for CO<sub>2</sub> capture with ultrafast
kinetics. Specifically, the nanowire powders exhibited an uptake of
0.35 g g<sup>ā1</sup> of CO<sub>2</sub> at an ultrafast adsorption
rate of 0.22 g g<sup>ā1</sup> min<sup>ā1</sup> at 650ā700
Ā°C. Lithium silicate (Li<sub>4</sub>SiO<sub>4</sub>) nanowires
and nanopowders were synthesized using a āsolvo-plasmaā
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
Li<sub>4</sub>SiO<sub>4</sub>āCO<sub>2</sub> reaction system.
The time scales for CO<sub>2</sub> 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, Li<sub>4</sub>SiO<sub>4</sub> nanowire powders showed
reversibility through sorptionādesorption cycles indicating
their suitability for CO<sub>2</sub> capture applications. All of
the morphologies of Li<sub>4</sub>SiO<sub>4</sub> 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 gā1 when charged to 4.7 V at a current of 20 mA gā1 and retains the capacity of 201 mAh gā1 after 100 cycles. It also exhibits an excellent rate capability of 138, and 114 mAh gā1 even at rates of 10 and 15 C (1 C = 240 mA gā1). 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 Ć 10ā10 cm2 sā1 and 2.1 Ć 10ā10 cm2 sā1, respectively