Principle –

They are based an principle of photovoltaic action i.e. conversion of light energy into (D.C.) electrical energy. A solar cell is simply a large photodiode operated in is photovoltaic mode.

Construction –

It is constructed in form of circular wafer with a very thin layer of p material at its surface. It consist of P-type and N-type semiconductor material forming P-N junction. The bottom surface is covered with a continuous conductive P-type contact to which a lead wire is attached. This surface is always away from the light. The upper surface layer of P-type material is extremely thin (0.5mm) so that light can penetrate into the junction. Silicon is commonly used. Another construction consist of P-type covered with a layer of N-type cadmium oxide (CdO2) to form junction. Power solar cells are also fabricated in flat strips to cover large surface area.

Working –

When the P-N junction is illuminated electron hole pairs are generated causing an electric field near the P-N junction by the positive & negative ions. Many of electrons are pulled across the junction due to electric field. This causes the (reverse) current to flow in the cell & through the external resistive load. Each cell provides about 0.5V at 150 mA.

Solar cells acts like battery when connected in series-parallel connection to give more power.