John L. Hodgkinson

Surface modification of aramid fibers by atmospheric pressure plasma-enhanced vapor deposition

Recent research results have indicated positive influences of inter-yarn friction on ballistic performance of woven fabrics and panels made from such fibers. The current investigation explores the effect of coating by means of atmospheric pressure plasma-enhanced vapor deposition with organic chemical (CH3)2Cl2Si on the inter-yarn friction. The scanning electron microscopy observations indicated that as the treatment time increases, more particles have been deposited on the surface of the fibers. The Fourier transform infrared spectra supported the existence of Si-O-Si vibration, which can be attributed to the chemical deposition. Energy-dispersive X-ray analysis further supported the deposition of the chemical compound. Experiments were carried out to evaluate the coefficients of static and kinetic frictions between the yarns and the results showed that the inter-yarn coefficient of static friction was increased from 0.1617 to 0.2969 and that of the kinetic friction increased from 0.1554 to 0.2436, as the treatment time increased to 4 minutes. In addition, there is evidence that the mechanical properties of the treated yarns were not negatively affected by the treatment.

Progression towards high efficiency perovskite solar cells via optimisation of the front electrode and blocking layer

The effects of a fluorine doped tin oxide (FTO) electrode, titanium dioxide (TiO2−x) blocking layer (BL) and perovskite (methyl ammonium lead triiodide) preparation on the overall properties of the photovoltaic cells have been studied. The FTO electrode was deposited by atmospheric pressure chemical vapour deposition (APCVD) and the hole blocking layer by spin coating, atomic layer deposition (ALD) or sputtering. We have shown the importance of obtaining uniform thin films of FTO, with low sheet resistance to aid the formation of pin hole free uniform TiO2−x blocking layers and hence well adhered, perovskite layers. The optimal BL thickness was 20 nm, while thicker films gave decreased shunt resistance and thinner a greater number of pin holes through the layers. We also showed that the conformal nature of ALD and magnetron sputtering, along with their increased uniformity control over spin coating again improved cell efficiency. The main improvement comes for the smaller Roc, attributed to an improved electrical transport through particularly the sputtered TiO2−x blocking layer. After identifying the optimised parameters, all the properties were combined to fabricate large solar cells (1 cm2) yielding power conversion efficiencies beyond 16%.

Optimization of Solar Cell Performance using Atmospheric Pressure Chemical Vapour Deposition deposited TCOs

High performance transparent conducting oxides, in particular doped SnO2, have significance for optimising photovoltaic cell performance. The surface morphology and resistivity are crucial to the performance of the final PV solar cell. There are three key objectives for the TCO properties. Firstly, the enhancing of optical scattering to improve efficiency of light absorption. Secondly, it is important to minimise absorption losses, as these impact directly on efficiency due to loss of photons available to the PV absorber layers. Thirdly, the TCO has to meet minimum conductivity requirements set by cell configuration designs. Typically these require about 10 Ohms/sq or less and so a TCO material capable of efficient doping, and a degree of nanostructure control for carrier mobility is sought for maximum performance.