Page 57 - Applied Photovoltaics

ª § qV · º
I I exp ¨ ¸ 1 » I L (3.1)
«
0
¬ © nkT ¹ ¼
where I L is the light-generated current.

The light has the effect of shifting the I-V curve down into the fourth quadrant where
power can be extracted from the diode, as shown in Fig. 3.4.
The I-V curve characterises the cell, with its power output being equal to the area of
the rectangle in the bottom right-hand quadrant of Fig. 3.4a. This I-V curve is most
often shown reversed, as in Fig. 3.5, with the output curve in the first quadrant, and
represented by
ª § qV · º
I I I exp ¨ ¸ 1 (3.2)
L 0 « »
¬ © nkT ¹ ¼

Figure 3.1. Behaviour of light shining on a solar cell. (1) Reflection and absorption
at top contact. (2) Reflection at cell surface. (3) Desired absorption. (4) Reflection
from rear out of cell—weakly absorbed light only. (5) Absorption after reflection.
(6) Absorption in rear contact.

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