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

Silicon-based solar cells – characteristics and production processes
consequence will be a decrease in the value of voltage at the cell’s terminals.
An increase of the N A value causes, in turn, a decrease of the charge carriers’ lifetime,
mainly due to the process of Auger recombination, affecting the decrease in the
intensity value of the current that is possible to be obtained from the cell. The cell
current flowing in the external unloaded circuit which shorts the front and the back
electrode will be a resultant of the photocurrent I ph generated by the absorbed
radiation reduced by dark currents I 1 , I 2 and current I r . The cell current I ph will be
originally the sum of the current generated in the space charge I SCR and the current
generated in the basis I B . This is schematically illustrated in Figure 7, where the area
of the space charge of width W is one which contains ionized donors and acceptors.
The existence of electron currents in the cell is a symmetric reflection of the
simultaneously occurring hole currents, with the basic difference of their size,
resulting from the fact that the thickness of the emitter does not exceed 0.5 μm and
the thickness of the base usually equals 200 μm. The photocurrent of the cell with the
p-type silicon will thus originate mainly from the minor carriers, which, in the base,
are constituted by the electrons.
Fig. 7. Scheme of electron current component of a solar cell. W is the width of the space
charge area and x c is the depth of the p-n junction’s position.
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