The Solar Cell

With the solar cell the effect of electron-hole generation is exploited.
It has been shown that a semiconductor shows better conductivity
at higher temperatures. That is, with increasing energy more bonds
are broken, and the free electrons contribute to electrical current.
Now, with the solar cell, light (commonly sun light) instead of
temperature is the energy source to generate electron-hole pairs.
The solar cell, conceptually a pn-junction, serves as a current
source, i.e. it is an active device!