Enhancement of light coupling to solar cells using plasmonic structures.

Photovoltaic technologies are likely to become one of the world’s major renewable energy generators in the future provided they are able to meet the increasing world energy demands at a significantly lower generation cost compared to conventional non-renewable energy sources. Photovoltaic systems based on 1st generation mono or poly crystalline silicon wafers have already been commercially successful over the past two decades. As the technology further develops however, it faces fundamental limits to further reduce cost which are primarily due to processing of silicon wafers. Hence, a 2nd generation of “thin film” photovoltaic systems, such as amorphous and poly silicon, CdTe and CIGS, which use cheap materials and inexpensive manufacturing processes with relatively high power conversion efficiency, have been developed. In order to commercialise the 2nd generation technology successfully, the efficiency of the thin film photovoltaic panels needs to increase to compete with the 1st generation silicon photovoltaics. Plasmonic structures provide a route to increase the efficiency of 2nd generation thin film photovoltaic devices. With the unique properties of plasmonic structures, such as ability to guide and trap light at nanometre dimensions, light absorption in the photoactive layer of thin film photovoltaic device can be increased resulting in improved device performance. In this research, plasmonic nanoparticles are utilised as an anti-reflection coating on the front side of the PV, coupling light into the active PV layer, and as scattering centres at the back reflector, increasing the path length of the light through the photoactive layer. The optical and electrical effects of the plasmonic structures are modelled simultaneously using a commercial technology computer aided design (TCAD) simulation package to understand and optimise the plasmonic effects on the performance of the 2nd generation thin film amorphous silicon, and 3rd generation organic, photovoltaic devices. The thesis describes the first ever dedicated optoelectronic model to simultaneously simulate optical and electrical properties of plasmonic thin film photovoltaics devices in collaboration with the TCAD software developer Silvaco Inc. The model demonstrates a maximum 12% relative increase in the power conversion efficiency of plasmon enhanced n-i-p configured amorphous silicon thin film photovoltaic devices. This remarkable increase in the performance is due to the light trapping in the photoactive layer of the thin film amorphous silicon photovoltaic devices, which results in improvements in the both the optical and electrical properties. Experimental work was also carried out to observe the plasmonic effects of the metal nanoparticles on the performance of 3rd generation organic photovoltaic devices which were subsequently modelled using the simulation package. A 4% relative increase in the efficiency was achieved using gold nanoparticles. A plasmonic organic photovoltaic device model and material library for the commercial organic semiconductor P3HT:PCBM, has also been developed and benchmarked experimentally. The model has assisted in the understanding of the effect of the plasmonic gold nanoparticles on the increased performance, as well as degradation effects due to the incorporation of silver nanoparticles