Solar Cells

Silicon solar cell efficiencies vary from 6% for amorphous silicon-based solar cells to 30% or higher with multiple-junction research lab cells. Solar cell energy conversion efficiencies for commercially available crystalline Si solar cells are around 14-16%. The highest efficiency cells have not always been the most economical - for example a 30% efficient multijunction cell based on exotic materials such as gallium arsenide or indium selenide and produced in low volume might well cost one hundred times as much as an 8% efficient amorphous silicon cell in mass production, while only delivering about four times the electrical power.

Organic solar cells and polymer solar cells are built from thin films (typically 100 nm) of organic semiconductors such as polymers and small-molecule compounds like polyphenylene vinylene, copper phthalocyanine (a blue or green organic pigment) and carbon fullerenes. Energy conversion efficiencies achieved to date using conductive polymers are as low as 4-5% for the best cells to date. However, these cells could be beneficial for some applications where mechanical flexibility and disposability are important.

Ternary I-III-VI compounds, members of the chalcopyrite semiconductor family, are promising solutions for the production of economically competitive photovoltaic energy. For example, Cu(In,Ga)(S,Se)₂ compounds reach conversion efficiencies of 22.5%. However, indium is rather rare in the earth crust. This problem limits strongly the expectation of maximum production of solar modules based on this material. As a consequence, it is very important to investigate the possibility to replace In with other more abundant elements, without losing the electronic properties that make this compound so attractive.

The challenges for material science related to the development of solar cells are on two levels: to study new materials created in a controlled way and to characterize the material in detail, especially with spectroscopic methods. In view of that, numerical simulations of structural, electronic and optical properties are extremely valuable in the design of advanced materials for photovoltaics.

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