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Demystification of the routes behind chemical deposition and growth of AZO films suitable for photovoltaics

Transparent conducting oxides are one of the most important constituents in modern thin film solar cells devices. Titanium oxide is widely used, but one of the major drawbacks is the necessity for the thermal treatment step that requires temperatures over 400 °C where zinc oxide arises as a viable alternative. ZnO can be easily derived in both mesoporous and nanostructured configurations by low cost, cheap, fast and non- toxic chemical methods. Furthermore, the properties can be improved by doping, primarily by aluminium in a cheap and efficient manner, in order to improve both electrical and optical properties. In this work we tried to address all feasible permutations of the synthesis steps by combination of sol-gel, hydrothermal and chemical bath deposition methods, with or without additional thermal treatments. The goal was to systematically compare the planar and nanostructured films, in both the effect of the morphology and the Al content on the end properties of the samples, and derivatively solar cells. The successfulness of the outcome was checked by grazing incidence X-ray diffraction, UV/VIS, Raman and Fourier transform infrared spectroscopy, scanning and transmission electron and atomic force microscopy. The electrical properties of the samples were studied in detail by means of solid state impedance spectroscopy and deep level transient spectroscopy. In conclusion, from the pragmatic point of view only few routes prove viable for preparing AZO films suitable for use in photovoltaic devices.

TCO ; AZO thin-films ; chemical bath ; wet chemistry ; GIXRD ; nanostructuring

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