Question

Difference between solar cell and photoconductive cell

Answer 1

A p-n junction photodiode can be operated under photovoltaic conditions similar to that of a solar cell. The current-voltage characteristics of a photodiode under illumination are also similar. But there are few major differences, such as:

1. For a photodiode, only a narrow wavelength range centred at the optical signal wavelength is important; whereas for a Solar cell, high spectral response over a broad solar wavelength range are required.
2. An important figure of merit for photodiodes is the quantum efficiency ( number of electron-hole pairs generated by incident photon), while the main concern for solar cells is the power conversion efficiency (power delivered to the load per incident solar energy.)
3. To work properly, photodiode operates in the third quadrant and the solar cell operates in the fourth quadrant of the I-V characteristics.
4. Photodiodes are small to minimise junction capacitance, while solar cells are large area devices.
5. Photodiodes are mainly designed to be operated in reverse bias whereas solar cells are designed to be operated in forward bias.