Mumbai university > FE > SEM 1 > Applied Physics 1

Marks: 5M

Year: Dec 2012

Solar cell:

Construction:-

• Solar cell is a p-n junction diode made up of crystalline silicon(Si).

• Phosphorous is used for doping the n-type layer and Boron for doping the p-type layer.

• Screen printed contacts are applied to the front and rear of the solar cell.

• The front end contacts are specially designed to allow maximun sunlight to fall on the semiconductor, but also accounting for minimum resistive losses.

• Each Si cell generates about 0.5V.

• Generally 36 cells are soldered together to produce a net 12V battery.

Working:-

• Under normal circumstances, the electrons occupy the lower energy level of the valence band.

• The higher energy level of the conduction band is not fully occupied.

• The difference between the energy levels is called band gap. $(E_g)$

• When a photon with greater energy than the band gap energy strikes the p-n junction, the electron gets excited and enters into the conduction band.

• At the same time, a hole is created in the valence band due to the electron’s migration to conduction band.

• As a result, an electron-hole pair is created.

  A potential gradient is obtained within the cell by connecting 2 types of semconductors, namely, type and n-type.

  Due to this, the excitation of electrons and generation of holes occur at junction interface.

• The gradient separates electrons and holes, and also keeps the current continuous when connected to the circuit.

• The potential difference resulting due to the separation of electron and holes is used to power the electric circuit or load.