Page 1015 - Basic Electrical Engineering

junction is varied. Thus, a photodiode can work as a photo-conductive device
like an LDR.

Figure 14.52 Photodiode with reverse-bias (only a very small reverse current flows across the
junction due to minority carriers)

14.13.6 Photovoltaic Cells or Solar Cells

A photovoltaic cell or a solar cell is a photodiode with no reverse bias voltage

applied across it. Even when the reverse bias voltage across a photodiode is
removed, the minority charge carriers continue to cross the junction when
light continues to fall on the p–n junction. Reverse current will continue to

flow through the circuit with the bias voltage removed but the circuit kept
closed as shown in Fig. 14.53 (a) and (b).

Electrons from the p-side (minority charge carriers) will flow to the n-side
and return to the p-terminal through the n-terminal of the device. This way

the device will work as a voltage source, i.e., a small voltage cell as shown in
Fig. 14.53 (c). p-Side is the positive terminal and n-side is the negative

terminal as has been shown. Thus, a junction-illuminated photodiode is a
photovoltaic cell
A solar cell is essentially a photodiode. A large number of photodiodes are

connected in series and parallel fixed on a panel so as to get considerable
voltage and current output. This way sun’s energy (solar energy) is converted

into electrical energy. Much research is being conducted to increase the