Thin film photovoltaics (PV) can potentially have a lower manufacturing cost by minimising the amount of a semiconductor material used to fabricate devices. Thin-film solar cells are typically only a few micrometres thick, while crystalline Silicon (c-Si) wafer solar cells are 180 - 300 micrometers thick. Incident light is not fully absorbed in such thin-film layers, resulting in lower energy conversion efficiency compared to c-Si wafer solar cells. Therefore, effective light trapping is required to realise commercially-viable thin film cells, particularly for indirect-band-gap semiconductors such as crystalline silicon. An emerging method for light trapping in thin film solar cells is the use of metallic nanostructures that support surface plasmons. Plasmon-enhanced light absorption is shown to increase cell photocurrent in many types of solar cells. This thesis presents the authors results on plasmonic polycrystalline silicon (poly-Si) thin film solar cells. It can be categorised into three parts, which are the optimum cells surface condition for nanoparticle (NP) fabrication, optimisation of Ag NP fabrication process to enhance energy conversion efficiency and a wet-etching method for re-using metallised polycrystalline silicon thin film solar cells after NP deposition. The first part (Chapter 3.2) introduces the optimum surface condition for silver NPs. NPs are formed on Si film, a native SiO2 and a thermal SiO2 layer, and absorption, scattering cross section and potential short-circuit current density are compared for varying surface conditions. The sample with NPs on the thermal SiO2 layer shows better absorption at 500 700 nm wavelength range, whilst the sample with NPs on the native SiO2 and with NPs directly on Si show higher absorption at greater than 700 nm. The sample with NPs on the native SiO2 layer indicates 62.5% potential short circuit current density enhancement, which is 0.7% and 12% higher enhancement than that of the sample with NPs directly on Si and NPs on the thermal SiO2 layer, respectively. The second part (Chapter 3.3) is a systematic study of optimisation of Ag NP fabrication process for enhancing efficiency of poly-Si thin film solar cells. Three factors are studied: the Ag precursor film thickness, annealing temperature and time. The thickness of the precursor film was 10, 14 and 20 nm; annealing temperature was 190, 200, 230 and 260°C; and annealing time was varied between 20 to 95 min. NPs formed from 14 nm thick Ag precursor film annealed at 230°C for 53 min result in the highest photocurrent enhancement, 33.5%, efficiency enhancement 32% and the plasmonic cell efficiency of 5.32% without a back reflector and 5.95% with the back reflector which is the highest reported efficiency for plasmonic poly-Si thin film solar cells. The last part (Chapter 3.4) introduces a wet-etching-based method for re-using metallised poly-Si thin film solar cells after NP deposition. Nitric acid is used to etch Ag NPs on the metallised cells. The optical and electrical properties of the metallised cell are compared before and after etching. The optical and electrical properties of the cell after etching are well matched with the initial value, and the Si film and the aluminium contacts are not damaged by the etching solution even after five times etching.
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