THIN FILM TECHNOLOGIES
The various thin technologies currently being developed reduce the amount of light absorbing material required in creating a solar cell. This can lead to reduced processing costs from that of bulk materials (in the case of silicon thin films) but also tends to reduce energy conservation efficiency, although many multilayer thin films have efficiencies above those of bulk silicon wafers. Another interesting aspect of thin film solar cells is the possibility to deposit the cells of all kinds of materials, including, flexible substrates which opens a new dimensions for new applications. Some of the materials for thin film are.
Cadmium Telluride: cadmium telluride is an effective light absorbing material for thin film solar cells. Compared to other thin film materials, cadmium telluride is easier to deposit and more suitable for large scale production. Despite the toxicity of cadmium telluride based solar cells, this is the only technology (apart from amorphous silicon) that can be delivered on large scale.
CIGS: CIGS are multilayered thin film composites. The abbreviation stands for copper indium gallium serenade. Unlike the basic silicon solar cell which can be modelled as simple p-n junction these cell are best described by a more complex hetero junction model. Higher efficiency can be obtained by using optics to concentrate the incident light. The use of indium increase the band gap of the CIGS layer, gallium is added to replace as much indium as possible due the relative more availability of gallium as compared to indium. Selenium permits for enhanced uniformity across the layer and so the number of recombination sites in the film are reduced which benefits the quantum efficiency and therefore the conversion efficiency.
CIS: CIS is an abbreviation for general chalcogenide films of copper indium solenoid. While these films can achieve 11/ efficiency; their manufacturing cost are high at present but continuing works is leading to more cost effective production processes.
GALLIUM ARSENIDE MULTIJUNCTION: HIGH EFFICIENCY cells have developed for special applications such as satellites and space exploration which require high performance. These multifunction cells consists of multiple thin films produced using molecular beam epitaxial. A triple junction cell consists of the semiconductors: gallium arsenide. Each type of semiconductor will have a charactistics band gap energy which causes it to absorb light most efficiently at a certain colour, or more precisely, to absorb electromagnetic radiations over a portion of the spectrum. The semiconductor is carefully chosen to absorb nearly all the solar spectrum, this generating electricity from as much of the solar energy as possible. Gallium arsenide multi junction devices are the most efficient solar cells to data, reaching as high as 39% efficiency.