Question

What is Solar Cell?

Answer

Solar Cell is basically a p-n junction which generates emf when solar radiation falls on the p-n junction. It works on the same principal (photovoltaic effect) as the photodiode, except that no external bias is applied and the junction area is kept much larger for solar radiation to be incident because we are interested in more power. A p-Si wafer of about 300 µm is taken over which a thin layer (~0.3µm) of n-Si is grown on one-side by diffusion process. The other side of n-Si is costed with a metal (back contact). On the top of n-Si layer, metal finger electrode (or metallic grid) is deposited. This acts as a front contact. The metallic grid occupies only a very small fraction of the cell area ( E_g)close to the junction: (2) separation of electrons and holes due to electric field of the depletion region. Electrons are swept to n-side and holes to p-side; (3) the electrons reaching the n-side are collected by the front contact and holes reaching p-side are collected by the back contact. Thus p-side becomes positive and n-side becomes negative giving rise to photovoltage.