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

Silicon-based solar cells – characteristics and production processes
been almost 30 years since the first solar cells were obtained, so far, there has been
no success in solving the basic problems causing the a-Si module efficiency to remain
at a relatively low level, of about 5 %, and also, after a few months of outdoor
operation, their photovoltaic conversion efficiency to drop down by about 15%. The
a-Si cells are produced with the PECVD method and, similarly to other thin-layer cells,
are obtained in the form of integrated modules. Due to the disordered crystalline
structure of amorphous silicon, E g is not strictly determined, although generally,
it assumes the values of 1,7 ÷ 1,8 eV [70]. For the absorption of the available spectral
range, a non-doped (i) a-Si:H-type layer, about 300nm thick, is introduced between
the thin doped ones. The illumination of the (i) a-Si:H layer causes, however, its
degeneration, as a result of the bonds breaking between the hydrogen and the
silicon, which effects a drop of the photovoltaic conversion efficiency of the cell. One
of the concepts are hybrid a-Si/µc-Si cells manufactured by Kaneka, Japan, which is
planning its production development at the level of 130 MW per year [6].
Fig. 35. Cross-section of a thin-layer cell made of amorphous silicon, with a typical kind of
conductivity and thickness of particular layers.
The basic drawback of all types of thin-layer cells, that is the cells whose active
layers are a few micrometers thick, are the difficulties in determining the standard
power and energy output, resulting from the metastable processes taking place in
their absorbers and causing a fluctuation of the initial parameters, under the effect of
many factors, such as the illumination time or the dark room storage time.
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