Silicon-based solar cells Characteristics and production processes ...

Silicon-based solar cells – characteristics and production processes
Fig. 28. Spectral distribution of solar radiation under conditions AM1.5, where P e is the
density of the solar radiation’s monochromatic flux.
The number of the air mass AMm is the function of the angle α, formed between
the direction of the Sun and the direction of the zenith, according to the dependence
m = (cosα) -1 . For the solar radiation beyond the earth’s atmosphere, the conditions
are described as AM0, and for the radiation at the sea level, where the Sun is in its
zenith, the conditions are AM1. In the case of crystalline silicon, the radiation with
the wavelength above 1,1 μm will not generate charge carriers, and thus it will be lost
for the solar cell. The spectrum availability for a given type of semi-conductor
material with the energy gap E g , that is the long-wave border, below which it is
possible for an electron to transfer from the valence band to the conduction band,
can be calculated from the following dependence:
where: h
c
– Planck’s constant
– light velocity
λ = hc/E g
(25)
The application of the above dependence allows for a significant increase of the
solar cell’s photoconversion efficiency with the use of materials of different energy
gap values E g . This principle is the basis for multijunction cells, usually produced on
the GaAs base, in which consecutive layers, placed from the rear to the front side of
the cell, possess progressively larger value of E g.
The measurements of the I-V characteristics are the more precise and unique, the
more the radiation spectrum of the solar simulator lamp resembles the actual
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