Page 67 - Applied Photovoltaics

ª § V IR · º V IR
I I I «exp ¨ ¨ s ¸ ¸ 1 » s (3.24)
L
0
« ¬ © q nkT ¹ » ¼ R sh
To combine the effect of both series and shunt resistances, the expression for FF sh ,
derived above, can be used, with FF 0 replaced by FF s (Green, 1992).

EXE RCI S ES
3.1 (a) Taking the silicon bandgap as 1.12 eV, and assuming unity quantum
efficiency as in Figs. 3.7 and 3.8, calculate the upper limit on the short
circuit current density of a silicon solar cell at 300 K for the standard
‘unnormalised’ global AM1.5 spectrum supplied in tabulated form in
Appendix B.
(b) Given that, near operating temperatures, the silicon bandgap
decreases by 0.273 mV/°C, calculate the normalised temperature
coefficient of this current limit at 300 K

1 dI
sc
I dT
sc
3.2 (a) A silicon solar cell (bandgap 1.12 eV) is uniformly illuminated by
monochromatic light of wavelength 800 nm and intensity
2
20 mW/cm . Given that its quantum efficiency at this wavelength is
2
0.80, calculate the short circuit current of the cell if its area is 4 cm .
(b) For the same quantum efficiency, what would be the value of this
current if the cell were made from a semiconductor of bandgap (i)
0.7 eV, (ii) 2.0 eV.
(c) For the silicon cell of part (a), calculate the open circuit voltage, fill
factor and energy conversion efficiency, given that its ideality factor
2
is 1.2 and dark saturation current density is 1 ȡA/cm .
(d) Estimate the range of values of (i) series resistance and (ii) shunt
resistance that would cause a relative reduction in the fill factor and
energy conversion efficiency of less than 5%.

3.3 (a) When the cell temperature is 300 K, a certain silicon cell of 100 cm 2
area has an open circuit voltage of 600 mV and a short circuit current
2
of 3.3 A under 1 kW/m illumination. Assuming that the cell behaves
ideally, what is its energy conversion efficiency at the maximum
power point?
(b) What would be its corresponding efficiency if the cell had a series
resistance of 0.1 ȍ and a shunt resistance of 3 ȍ?

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