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5.2.1 Definition

A solar cell or photovoltaic cell is a device that converts solar energy into electricity thanks to the photovoltaic effect. The workhorse photo­voltaic material, silicon, performs this conversion fairly efficiently, but silicon cells are relatively expensive to manufacture. Some other semiconductors, which can be deposited as thin films, have reached market, but although they are cheaper, their efficiency does not compare to that of silicon. Therefore, other technologies such as multi-junction cells have been developed. Solar cells are thus classified into three generations. At present there is concurrent research into all three generations while the first generation technologies are most highly represented in commercial production.

Efficiency vs. cost for the 3 solar cells generations

First Generation

First generation cells consist of large-area, high quality and single junction devices. Those technologies involve high energy and labour inputs which prevent any significant progress in reducing production costs. Single junction silicon devices are approaching the theoretical limiting efficiency of 33% and achieve cost parity with fossil fuel energy generation after a payback period of 5-7 years.

Second Generation

Second generation materials have been developed to address energy requirements and production costs of solar cells. The most successful second generation materials have been cadmium telluride (CdTe), copper indium gallium selenide (CIGS), amorphous silicon (a-Si) and micromorphous silicon. These technologies do hold promise of higher conversion efficiencies, particularly CIGS-CIS. Dye Sensitized Solar Cell and CdTe offers significantly cheaper production costs. There is certainly a trend toward second generation technologies however commercialisation of these technologies has proven difficult.

Third Generation

Third generation technologies aim to enhance poor electrical performance of second generation thin film technologies while maintaining very low production costs. This solar cell generation is still at a laboratory stage. But current research is targeting conversion efficiencies of 30-60% while retaining low cost materials and manufacturing techniques.

[i] "Bright outlook for solar cells"; E. Cartlidge: Physics World 20, 20 (2007)

[ii] "Third-generation photovoltaics"; G. Conibeer: Materials Today 10, 42 (2007)