Question

What is the main problem of a solar cell made of a single layer pure or pristine semiconductor (such as the first Selenium based solar cell)? Why PN junction cell is much better?

please answer both parts.

Answer 1

Hey!

On a general note, an extrinsic semiconductor (semiconductors that are doped) have a better conductivity and performance ina relatively lower temperature to conduct electricity than that of the pure form of semiconductor. That is because the band gap between the conduction and the the forbidden gap is very much high in pristine semiconductor materials than that of the doped.

When a single layer or a single type of material is been used as the semiconductor material for the solar cell, when the packets of energy (photons) hit it's surface, the formation of the depletion layer to create a potential difference for the conduction is very small.  Hence less conversion of electricity and less efficient.

Where else, in a PN junction cell, the depletion layer between the the thin N layer and the the P type material is huge. Hence resulting with a better conduction through the bigger depletion layer. Hence the potential difference formed can be huge, thus allowing good flow of electricity with better efficiency.