Transactions on Engineering Technologies by Unknown

Author:Unknown
Language: eng
Format: epub
ISBN: 9789811568480
Publisher: Springer Singapore

1.1 Thin Film Solar Cells and Metal Oxide Solar Cells

Thin-film solar cells are the basis for nearly all the presently available commercial solar cells. Thin film solar cells attempt to bridge the cost disadvantages of silicon wafers by using thin films of semiconductors that are usually deposited onto a supporting substrate. The active layers are usually thin yet able to absorb large amounts of incident solar radiation due to the material’s strong absorption capacity [18].

Thin-film solar cells have been deposited using a variety of techniques onto different substrates (metal or non-metal, flexible or rigid) to produce a variety of layers (absorber, contact, buffer, anti-reflection) [19]. This flexibility makes it easy for thin films and engineering of layers to be fine-tuned in order to improve device performance. Thin film solar cells can be further developed to produce a tandem-structure approach called the integrated-tandem-Solar-Cell (ITSC) system. Metal oxides are a highly sought after candidate for a variety of technological applications due to their special and tuneable properties. They have excellent optical, optoelectronic, magnetic, mechanical, and thermal properties, among other properties [20].

Nickel oxide (NiO) is one of the least researched metal oxides yet with promising properties in optoelectronic applications. It can be obtained as black or green crystalline powder having a density of 6.67 g/cm3 and melting point of 1955 °C with chemical composition of nickel being 78.55% and oxygen 21.40% with a molar mass of 74.6928 g/mol, magnetic susceptibility of to 6 cm3/mol and refractive index of 2.1818 [21]. Nickel oxides exist in various oxidation states viz nickel trioxide or sesquioxide (Ni2O3), nickelous oxide (NiO), nickel dioxide (NiO2), nickelosic oxide (Ni3O4) and nickel peroxide (NiO4) [22]. Amongst these, NiO has rhombohedral or cubic structure and possesses a pale green colour. The stoichiometry of NiO is roughly indicated by the colour of the sample [23]. NiO is a p-type semiconductor having wide band gap from 3.5 eV to 4.0 eV [24] with excellent chemical stability. It also has excellent durability and electrochemical stability with a large range of optical densities owing to good optical, electrical and magnetic properties. A versatile material with multiple applications in: solid oxide fuel cells (nickel cermet), lithium ion micro batteries (lithium nickel oxide cathode), electrochromic coating, in aerospace as a light weight structural component, as a catalyst, as anti-ferromagnetic layers, as adhesive, p-type transparent conductive films, materials for gas or temperature sensors such as CO sensors, H2 sensor, and formaldehyde sensors and the p-type layer for UV detectors [5–7, 25]. Also, sintered nickel oxide is used for producing nickel steel alloys which won the 1920 Nobel Prize in Physics for Charles Guillaume. NiO is used in the Edison battery (nickel-iron battery) and is used to make NiCd rechargeable batteries which were used in many electronic devices until the advent of the NiMH battery.

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