2 in 1 solar street light 30w solar battery knowledge:

Although semiconductors have photoconductivity, they cannot purchase energy. After the semiconductor is irradiated with light, the carriers increase, but without the external power source, the carriers cannot move to the electrodes. If the built-in electric field of the pn junction is used, even if an external power source is provided, electrons generated by photoexcitation are separated from hole carriers, and light can be generated.

When a p-type and an n-type semiconductor are combined into an n-junction diode, an energy gradient is generated in the p-depletion layer. The slope of this energy gradient is the electric field, which is the built-in electric field. By illuminating the diode with light, the electrons move from the valence band to the conduction band in a certain direction, creating pairs of electrons and holes. That is, current can be generated without an external power supply.