8. SEMICONDUCTOR MATERIALS FOR PHOTOVOLTAIC DEVICES

A solar cell is a photoelectric converter. It converts photons into electrical energy.

• maximum electrical output power under standard illumination

• Example for Germany 10 kWp

• The solar spectrum corresponds approximately to a black body radiation with a temperature of 5800 K

• The power by solar irradiation at AM 1.5 is 1 kW/m2

• In central Europe (Germany), PV modules with 1 kWp can produce ≈1000 kWh of electric energy per year

• The contribution of solar cells to electricity generation continuously increases all over the world

• A solar cell converts light into electric energy by separation of electron-hole pairs

• The current-voltage curve of the illuminated diode corresponds to that of the non-illuminated diode shifted on the current axis by the photocurrent (if the photocurrentis independent on voltage)

• The efficiency of the solar cell is given by the product of the open circuit voltage, theshort circuit current and the fill factor, divided by the incident light intensity

• The photocurrent corresponds to the number of absorbed photons and decreaseswith the band gap of the semiconductor

• The photovoltage of a p-n diode solar cell increases linearly with the band gap

• The theoretical efficiency (Shockley-Queiser-limit) has a maximum of 30% for bandgaps of 1.2-1.5 eV