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Solar cell

Photovoltaics allows direct conversion of sunlight into electrical energy. Conversion takes place without any emissions and material flows inside the solar cell. The efficiency of solar cells is given as a percentage. Efficiency is the ratio of electrical energy generated and the amount of incident light.

Solar cells are distinguished by their substrate material: crystalline solar cells and thin-film cells. Crystalline cells (currently) consist of monocrystalline (mc-Si) or polycrystalline (pc-Si) silicon and have the highest level of efficiency. The cells can be contacted on the front or back. Applying the contact on the back reduces or completely eliminates the contact grid on the front, thus reducing shadowing effects and thereby increasing efficiency (idw-online 2009).

Currently there are three different thin-film cell technologies available on the market: silicon-based (amorphous silicon: a-Si; a combination of a-Si and microcrystalline silicon a-Si/µc-Si), cadmium telluride (CdTe), and copper indium diselenide (CIS, CIGS). Research is also ongoing on a host of other thin-film cells and organic or dye-sensitised cells, that will come onto the market in the next few years with the promise of major cost reductions for PV systems.

Both types – crystalline cells and thin-film cells – have their merits:

Table 1: Comparison of crystalline cells and thin-film cells
Cell type Advantages Disadvantages
Crystalline High, stable cell efficiency
mature cell technology (years of experience)
Variety of colours and forms 
Limited flexibility (cell grid)  Inhomogeneous appearance  No homogeneous transparency  Complex, time-consuming cell/module production
Thin film Lower system costs
homogeneous appearance
Variety of colours and forms
(As yet) lower levels of efficiency  Less experience with regard to long-term stability
The table presents the main characteristics of typical solar cells.
Table 2: Typical solar cell characteristics
Cell monocrystalline polycrystalline thin-film
Size commonly: 
125 x 125 mm,
156 x 156 mm
125 x 125 mm,
156 x 156 mm
almost any substrate format
Form rectangular, square, pseudo-square (with rounded corners) rectangular, square
any substrate format
Colour usually black
usually crystal-blue black, reddish-brown or dark-green
Efficiency currently up to approx. 21% currently up to approx. 16% currently up to approx. 13%
Figure 1: Examples of monocrystalline solar cells
Figure 2: Example of monocrystalline back-contact cell

Source: solar-designs 2009, 2009

Figure 3: Examples of polycrystalline solar cells
Figure 4: Polycrystalline back-contact solar cell (example)
Figure 5: Examples of thin-film cells

Last page update: 04.02.2011