High-performance amorphous silicon solar cells with plasmonic light scattering

This research project is focused on the process optimisation and optical enhancement of the hydrogenated amorphous silicon solar cell design, achieved by the incorporation of light scattering plasmonic nano-particles. These treatments consist of a very thin layer of finely tuned silver metal-island films, which preferentially scatter light within a wavelength range tailored to the device absorption characteristic. This serves to increase the optical path length without the need for surface texturing of the semiconductor material. Within this study, the PECVD process is used to explore the parameter space and fabricate silicon thin films with excellent optical and electrical performance, and a P-I-N amorphous silicon device structure is fabricated with a high performance of 6.5% conversion efficiency, 14.04mA/cm2 current density and 0.82V open circuit voltage.The effects of metallic nano-particle arrays is demonstrated by numerical simulation, showing that variations in particle size, shape, position within the structure and surrounding material greatly influence the enhancement of the nano-particles on silicon absorber layers, and that particles positioned at the rear of the device structure adjacent to a back reflector avoid absorption losses which occur below the particle resonance frequency when such structures are positioned at the front surface. It is shown than an improvement in optical absorption of just over 1% is possible using this method.Silicon thin films are fabricated with self-organised nano-particle arrays via means of annealed metal films, positioned at the front or back adjacent to a metallic reflector, and measurements of optical transmittance, reflectance and absorption are taken. The optimum annealing temperature and duration is identified, and it is shown that these variables can greatly affect the absorption of the device stack. To conclude the study, an amorphous silicon P-I-N photovoltaic device is fabricated featuring self-organised nanoparticle arrays within the back reflector, and a modest improvement of energy conversion efficiency is observed with scope for further optimisation and enhancement