Solar Cell- Working Principle
Solar cells, or photovoltaic cells, transform light, usually sunlight, into electric current. Few power-generation technologies are as clean as photovoltaics (PV).
These section explains the solar cell in brief.
Structure & Working Of the Solar Cell:
- To utilize a maximum amount of available optical energy, it is necessary to design a solar cell with a large area junction located near the surface of the device.
- The planar junction is formed by diffusion or ion implantation, and the surface is coated with appropriate materials to reduce reflection and to decrease surface recombination.
- In the device shown in Fig, for example, the junction depth d must be less than Lp in the n material to allow holes generated near the surface to diffuse to the junction before they recombine.
- Similarly, the thickness of the p region must be such that electrons generated in this region can diffuse to the junction before recombination takes place.
- This requirement implies a proper match between the electron diffusion length Ln, the thickness of the p region, and the mean optical penetration depth 1/α.
- It is desirable to have a large contact potential V0 to obtain a large photovoltage, and therefore heavy doping is indicated; on the other hand, long lifetimes are desirable and these are reduced by doping too heavily.
- It is important that the series resistance of the device be very small so that power is not lost to heat due to ohmic losses in the device itself.
- A series resistance of only a few ohms can seriously reduce the output power of a solar cell.
- Since the area is large, the resistance of the p-type body of the device can be made small.
- However, contacts to the thin n region require special design.
- If this region is contacted at the edge, current must flow along the thin n region to the contact, resulting in a large series resistance.