Principle of solar cell power generation

In the P-type semiconductor, some atoms close to the PN intermediate line lose their holes and become negative ions. Some of the atoms near the PN intermediate line in the N-type semiconductor lose electrons and become positive ions; The contact between the P-type semiconductor and the N-type semiconductor forms a spatial load zone.

In the space loading region, the negative ions in the left P region and the positive ions in the right N region will form a self-built electric field and generate electric field force. The direction of the current is the green arrow, and the hole will move from right to left due to the electric field force, and the electron will move from left to right due to the electric field force, and yes that's the drift of the electron and the hole that we said above; It can be found that the drift is equivalent to the electrons and holes that have just diffused past drifting back, so eventually when the drift and diffusion motion reach equilibrium, the middle space current carrying region will tend to be stable, forming a PN junction.

PN junction is actually a diode, with one-way conductivity, in its external positive power supply (positive N, negative P), the same direction as the self-built electric field, electron and hole drift will increase, PN width is reduced, the current can flow smoothly, it should be the meaning of small resistance; When the negative power supply is connected externally (positive P, negative N), in the opposite direction of the self-built electric field, the diffusion of electrons and holes will increase, the PN junction region will increase, the current can not pass smoothly, and the resistance will eventually tend to be infinite. (That is, positive connection can be powered on, reverse connection can not be powered on)

5. Photovoltaic effect

Finally to the end, recall that under the external stimulation of the semiconductor, the electrons bound by the nucleus can cross the forbidden band from the valence band into the conduction band, becoming free electrons, flying themselves.

Our sunlight is this stimulus, when the sun shines on the above large semiconductor composed of P-type and N-type semiconductors, there are three regions of atoms will be affected by photons, produce a transition reaction, forming electron hole pairs, respectively: The PN junction region, the P-type and N-type semiconductor region other than the PN junction, is that every place in the whole block may produce electron hole pairs. As shown below:

The electrons generated by light on the PN junction will be thrown into the N-type region due to the influence of electric field force, and the holes generated on the PN junction will be thrown into the P-type region due to the influence of electric field force. There are a few electron holes on the edge of the PN junction may also pass through the PN junction, but it should be unlikely; At this point, the solar cell has been formed, and a circuit is connected to both ends of the semiconductor to generate an electric current. This is solar cell power generation!

To conclude:

1. First, trivalent and pentavalent elements are doped in the intrinsic semiconductor to form a P-type/N-type semiconductor. (That is, when making silicon wafers, doping to form P-type/N-type silicon wafers)

2. P-type and N-type semiconductors are put together to form PN junctions due to the diffusion of many sons and the drift of few sons. (When making a battery chip, it will be further doped on the silicon chip to form a PN junction)

3. When light is irradiated in PN junction, electrons transition from valence band to conduction band, forming free electrons and holes, and move to N and P under the influence of electric field force, the external loop can form a current.