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

Silicon-based solar cells – characteristics and production processes
I sh - leakage current
R sh - cell’s parallel resistance
A 1 - diode’s quality coefficient (value close to 1)
A 2 - diode’s quality coefficient (value close to 2)
R - external resistance
Parameter I sc is described as the short-circuit current, and V oc is the voltage of the
open circuit. The I-V characteristics presented in Fig. 25 include the points which
determinant for the cell’s photovoltaic conversion efficiency E ff . The value of P m =
I m ∙V m is the maximum actual power possible to be obtained from the cell, but always
lower than the ideal maximum power being a product of I sc ∙V oc , which is expressed by
the filling factor FF in the relation [17]:
I V P
FF =
I V I V
m m m
= (23)
sc
oc
sc
oc
Knowing the above I-V characteristics, one can calculate the basic and most
important value for the solar cell, which is the value of its photovoltaic conversion
efficiency E ff , often described as the cell efficiency, according to the following formula
[17]:
E
ff
IscVoc
= FF ⋅100%
(24)
P A
in
0
where: P in - intensity of radiation falling on the cell [W/m 2 ]
A 0 - cell’s surface area [m 2 ]
This is one of the most important quantities determining the market price of the
cells sold as commercial product, whose value is given in Euro (€) or USD ($) per watt
of the cell power. The decisive factors for the shape of the I-V characteristics are the
quantities R s and R sh , which is presented in Fig. 27, with the following marked values:
P m (R s ) – maximum cell power with excessive R s , P m (R sh ) – maximum cell power with
deficient R sh .
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