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2. PHD Thesis / Tesis PHD
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Title:	Development of high quality low cost transparent conducting thin films for cadmium telluride (CDTE) solar cells
Authors:	Mohammed Mannir Aliyu (P52366)
Supervisor:	Nowshad Amin, Professor Dr.
Keywords:	High quality low cost transparent conducting thin films Transparent conducting thin films Thin films Cadmium telluride CDTE Solar cells
Issue Date:	17-Dec-2012
Description:	Transparent conducting thin films are class of materials that find wide range of applications in devices requiring high transparency and good electrical conductivity. Among the areas of applications of these materials, thin film solar cells are the prominent, where they serve as front contact layers. However, these materials have limited conductivity and higher costs that lead to reduced performance of the solar cells. Thus, in order to overcome these limitations, there is the need to develop fabrication processes to produce high quality transparent conducting films with high transparency and good electrical conductivity. RF magnetron sputtering has been identified as the most suitable deposition method for such transparent conducting oxides (TCO) due to its good film uniformity, control, reproducibility and ease of industrial scaling. This work attempts to produce high quality TCOs using RF sputtering by optimizing all the deposition variables, until optimal film properties are obtained. Three kinds of TCO materials, indium tin oxide (ITO), aluminum zinc oxide (AZO) and fluorine doped tin oxide (FTO) have been investigated in this study. While detailed investigation was carried on ITO, only general study was made on AZO, and preliminary investigation was done on FTO. The results show that by using high deposition temperatures, low RF power, good quality ITO films can be produced, without thermal treatment/annealing. Alternatively, moderate deposition temperatures and moderate RF power followed by annealing at 450 oC for only 15 minutes produces, almost equally good films. Films with highest transmittance of 90% and lowest resistivity of 7.56x10-5 Ω-cm have been obtained, being the lowest resistivity reported for sputtered ITO films, to date. When compared to commercial ITO, the films in this work show larger grain size, higher carrier concentration and mobility, resulting in much higher conductivity. Results of high vacuum anneal (HVA) indicate that only films deposited at low to moderate temperatures show improved conductivity after anneal, while those deposited at high temperatures show degraded post annealed conductivity. Meanwhile, AZO films achieved highest transmittance of over 90 % and lowest resistivity of 56 x10-4 Ω-cm. The preliminary investigation of FTO produced films with lowest resistivity of 26.3 x10-3 Ω-cm and transmittance of 94 %. As for application, when CdS was deposited on these films and on both commercial ITO and FTO, samples on our films produced CdS of larger grain size, smoother surface, higher transmittance as well as better conductivity. Conversely, when our ITO was deposited on CdS, its electrical indices improved compared to that on glass. Based on these results, complete CdTe solar cells were fabricated on glass, polyimide (PI) and molybdenum substrates, in both superstrate and substrate configurations. The superstrate cell on glass produced the highest efficiency of 4.28 % and Jsc of 23.72 mA/cm2, Voc of 0.576 V, FF of 0.313, while the substrate cells on Mo have 3.80 % efficiency, Jsc of 19.40 mA/cm-2, Voc of 0.58 V and FF of 0.34. However, cells on PI have lowest performance with best efficiency of 1.08 %, 12.71 mA/cm2 Jsc, 0.34 V Voc and 0.25 FF. Although these cells have moderately high values of Jsc and Voc, but low efficiencies. This is attributed to the low values of FF, suspected to be due to the poor back contacts, which have not been optimized. In conclusion, this work has shown, successfully, the feasibility of developing high quality TCO using RF sputtering by RF sputtering technique.,PhD
Pages:	240
Call Number:	TA418.9.T45 .A445 2012 3
Publisher:	UKM, Bangi
Appears in Collections:	Faculty of Engineering and Built Environment / Fakulti Kejuruteraan dan Alam Bina

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