Abstract-Optical losses at the front surface of a silicon solar cell have a significant impact on efficiency, and as such, efforts to reduce reflection are necessary. In this work, a method to fabricate and passivate nanowire-pyramid hybrid structures formed on a silicon surface via wet chemical processing is presented. These high surface area structures can be utilised on the front surface of back contact silicon solar cells to maximise light absorption therein. Hemispherical reflectivity under varying incident angles is measured to study the optical enhancement conferred by these structures. The significant reduction in reflectivity (<2%) under low incident angles is maintained at high angles by the hybrid textured surface compared to surfaces textured with nanowires or pyramids alone. Finite Difference Time Domain simulations of these dual micro-nanoscale surfaces under varying angles supports the experimental results. In order to translate the optical benefit of these high surface area structures into improvements in device efficiency, they must also be well passivated. To this end, atomic layer deposition of alumina is used to reduce surface recombination velocities of these ultra-black silicon surfaces to below 30 cm/s. A decomposition of the passivation components is performed using capacitance-voltage and Kelvin Probe measurements. Finally, device simulations show power conversion efficiencies exceeding 21% are possible when using these ultra-black Si surfaces for the front surface of back contact silicon solar cells.
A Schottky diode-based sensor is a promising structure for high sensitive and low power sensor. This paper investigates a device called back-to-back Schottky diode (BBSD) for humidity sensing operation. The BBSD provides simpler device configuration that can be fabricated using less complicated process. The current-voltage characteristic of the fabricated BBSD was measured at different relative humidity. From the obtained characteristics, series resistance, barrier height and ideality factor was analyzed. The device current increased at higher humidity level. The current increase could be associated to the decrease in series resistance, barrier height and ideality factor. When humidity decreased from 11% to 97%, the barrier height showed reduction of 0.1 eV. The barrier height reduction was explained by considering electric field-induced reduction of graphene oxide. The observed result confirmed the device feasibility as promising simple and low cost humidity sensor.
Abstract-In this work we present morphological and electrical characteristics of a junction formed of Si P-type films deposited on an N-type silicon wafer using a hot wire chemical vapour deposition tool. We describe the fabrication process, and study the influence of diborane flow and post-process annealing in improving junction characteristics. Our morphological studies undertaken using atomic force microscopy show that the initial deposition suffered from voids rather than being a uniform film, however this improves significantly under our annealing treatment. The improvement in morphology was observed in the electrical characteristics, with estimated Voc doubling and rectification of the junction improving by several orders of magnitude. Fitting of the current-voltage curves to a two diode model, showed that increasing the diborane flow in the process helps reduce the saturation current and ideality factors, whilst increasing the shunt resistance. ECV and QSSPC measurements are used to characterise the deposited films further. A solar cell device with a silicon epitaxy emitter is modelled using industry standard 3D modelling tools and input parameters from experimental data, and the impact of defects is studied. A potential efficiency approaching 25% is shown to be feasible for an optimised device.
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