K. Bass

Methods for the reduction of shape change and dendritic growth in zinc-based secondary cells

Abstract The widespread adoption of alkaline zinc-based secondary systems has been hindered by two inherent problems associated with the charge reaction. These are commonly referred to as shape change and dendrite growth. This review examines the attempts that have been made to lessen their effects and, hence, ultimately arrive at a working, cycleable secondary zinc-based battery.

Pinhole free thin film CdS deposited by chemical bath using a substrate reactive plasma treatment

Achieving a pinhole-free CdS layer is necessary to produce high performance thin film CdTe solar cells. Pinholes in the CdS layer can compromise the efficiency of a CdTe solar cell by causing shunts. We have investigated the use of a plasma treatment of a fluorine doped tin oxide coated glass substrate (NSG TEC 15) and its effect on pinhole reduction in thin film CdS layers grown by Chemical Bath Deposition. CdS films, <100 nm thickness, were deposited on both O2/Ar plasma cleaned and conventionally cleaned substrates. We show that the O2/Ar plasma treatment of the TEC 15 substrate reduced the water contact angle from ∼55° to less than 12° indicating a substantial increase in the surface energy. The CdS deposited on the plasma treated TEC 15 was pinhole free, very smooth and homogenous in morphology and composition. Scanning electron microscopy images show that the O2/Ar plasma treatment is effective in increasing film density and grain size. Corresponding spectroscopic ellipsometry measurements show an i...

The performance of secondary zinc electrodes in modified alkaline electrolytes I. Galvanostatic passivation studies in alkaline electrolyte

Abstract The passivation characteristics of a planar zinc electrode have been examined in 2 M KOH electrolytes containing a variety of additions. The time to passivation has been measured and compared to that of a planar cadmium electrode in 5.3 M KOH. The most promising additives were found to be borate and chromate. Auger analysis of electrode surfaces revealed possible passivating mechanisms.

The electrodeposition of zinc onto graphitic carbon substrates from alkaline electrolytes

Abstract The electrodeposition and dissolution reactions of zinc on both solid and pasted graphitic substrates, in a series of KOH electrolytes containing zincate, have been studied using cyclic voltammetry. The data acquired have been used to aid the interpretation of the effects of graphitic additions on the charge and discharge reactions of conductor-modified secondary cells with zinc anodes.

Optimising the performance of an optically controlled microwave switch

Optical control of microwave switches is an appealing concept for use in reconfigurable antennas as it eliminates the need for metallic biasing lines which may affect the performance of the wireless system. The ultimate goal of this study is to minimise insertion loss of a photoconductive microwave switch in the ON state whilst maintaining high isolation in the OFF state. Firstly, a parameter simulation study using different substrate materials, thicknesses and gap widths is presented to obtain optimised S21 results. The best performance is from a 1.2mm line using a 0.3mm gap. Secondly, the effect of passivation and texturisation on the photoconductivity and microwave performance of the silicon die is investigated. Passivation of the sample decreases insertion loss, however texturing the surface increases loss.

Electrochemical investigation of lead-calcium alloys in sulphuric acid

The hydrogen evolution reaction from, and the cycle life (Pb /ar PbSO4) of, a series of lead-calcium alloys (0 - 0.2 wt.% Ca) in sulphuric acid hav The exchange current density and Tafel slope for the H.R.E. increase with Ca content up to 0.05 wt.% then decrease to a value approaching that of pure The observed results are explained by: (i) preferential adsorption of calcium ions at the electrode surface; (ii) incorporation of Ca, to form a supersaturated solution, with alloys containing < 0.075 wt.% Ca; (iii) formation of an insoluble, non-conducting layer of calcium sulphate on the high content alloy.

Metrology of silicon photovoltaic cells using Coherence Correlation Interferometry

Surface metrology plays an important role in the development and manufacture of photovoltaic cells and modules. Coherence Correlation Interferometry (CCI) is a non-contacting surface metrology tool with potentially important applications in the characterization of photovoltaic devices. Its major advantages are that it is fast, non-destructive and it takes its data from a relatively large and hence representative area. A special mode, called “stitching x-y” can be used to provide information on a wider area, combining measurements taken in different zones of the sample. The technique is capable of providing surface roughness and step height measurements with sub-nanometre precision. It is also capable of measuring quantitatively surface texture and surface form in three dimensions and it now has a new capability to measure thin film and thick film thickness. CCI measurements are presented on a range of features on silicon photovoltaic cells including surface roughness, surface texture, the profile of laser grooves for buried contacts as well as the roughness and thickness of silicon nitride thin films. Complementary analysis using spectroscopic ellipsometry is also presented for verification. CCI is a sensitive, non-destructive metrology technique with potential use as an in-line quality assurance tool in the large scale production of photovoltaic modules.

Passivation of laser grooved buried contacts (LGBC) solar cells with silicon oxide or silicon nitride grown by a remote sputtering deposition system

Silicon nitride (SiNx) and Silicon Oxide (SiO2) thin films have been deposited by a new remote plasma deposition system HiTUS (High Target Utilisation Sputtering). The remote plasma geometry allows, pseudo separation of plasma/target-bias parameters, avoiding ion bombardment, and effectively eliminates poisoning, making it an attractive option for stable reactive sputtering of important electronic and photovoltaic films including SiNx or SiO2 for passivation of the front surface or as antireflective coating. The SiNx (SiO2) thin films are grown by reactive sputtering from a silicon target in an Ar/N2 (O2) atmosphere, negating the use of silane gas in difference to the more commonly used PECVD method. A deposition rates up to 7.8 Å/s have been obtained (see Fig.1).The deposition rate increase from 4 Å/s up to 7Å/s at 100% RF bias power with an error of ±5%. A good control of the refractive index (between 1.7 up to 2.3) has also been found. Photo conductive measurements by a WCT-100 were performed on silicon wafer after each thermal process to measure the effective lifetime of p-type crystalline silicon wafer Boron doped ≪100≫ to measure the effective lifetime of the minority carriers. Carrier lifetime up to 30 microseconds have been measured on c-Si wafer passivated by SiO2. We have shown that the SiO2 and SiNx thin film have high passivation quality making the HiTUS a viable new sputtering system for deposition of antireflective coatings for solar cells production.