A solar cell is a junction diode. A very thin layer of p-type semiconductor is grown on a…

A solar cell is a junction diode. A very thin layer of p-type semiconductor is grown on a relatively thicker n-type semiconductor, having a few finer electrodes on the top of the p-type semiconductor layer. These electrodes do not obstruct light from reaching the thin p-type layer. Just below the p-type layer, there is a p-n junction. We also provide a current-collecting electrode at the bottom of the n-type layer. Similarly, the holes in the depletion can quickly come to the p-type side of the junction. Once the newly created free electrons come to the n-type side, they cannot further cross the junction because of the barrier potential of the junction. Similarly, the newly created holes once they come to the p-type side cannot further cross the junction because of the same barrier potential of the junction. As the concentration of electrons becomes higher on one side, the p-n junction will behave like a small battery cell. A voltage is set up which is known as photovoltage. If we connect a small load across the junction, there will be a tiny current flowing through it. The I-V characteristic of solar cells is given in the figure. What is the suitable band gap of the semiconductors used as solar cell materials?