Page 53 - Applied Photovoltaics

Figure 2.11. The diode law for silicon—current as a function of voltage for
temperatures T 1 and T 2 (T 2 > T 1). For a given current, the curve shifts by
approximately 2 mV/°C.

EXE RCI S ES
–1
6
2.1. The absorption coefficient of silicon decreases from 1.65×10 cm at 0.3 ȝm
–1
–1
wavelength, to 4400 cm at 0.6 ȝm and 3.5 cm at 1.1 ȝm. Assuming zero
reflection from both front and rear surfaces at each wavelength, calculate and
sketch the generation rate of electron-hole pairs, normalised to the surface
generation rate, across a silicon cell of 300 ȝm thickness.
2.2. In terms of the electronic properties of semiconductors, explain why the
absorption coefficient increases with increasing photon energy, for energies
near the semiconductor bandgap (see Green, 1992 or similar for further
information).

REFE RE NCES

Basore, P.A. (1994), ‘Defining terms for crystalline silicon solar cells’, Progress in
Photovoltaics: Research & Applications, 2, pp. 177–179.

Becquerel, E. (1839), ‘Memoire sur les effets electriques produits sous l’influence es
rayons solaires (Note on the electric effects produced under the influence of
sunlight)’, Comptes Rendus Hebdomadaires des Séances de l’Académie des Sciences,
IX, pp. 561–567; ‘Recherches sur les efféts de la radiation chimique de la lumière
solaire, au moyen des courants électriques (Studies of the effect of actinitic radiation
of sunlight by means of electric currents)’, Bibliotheque Universelle de Geneve,
XXII, pp. 345–366.

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