Q.Explain the working principle of a solar cell. Mention its applications.

Step 1 (Working principle). A solar cell (photovoltaic cell) is essentially a large-area p-n junction -- a thick p-type silicon base with an ultra-thin n-type layer on top forming the junction (or the reverse arrangement for an n-type cell) -- designed to generate an emf directly from absorbed light, needing no external bias at all.

Step 2. The underside of the p-silicon base is coated with metal for the back electrical contact, the top n-type layer carries a metal grid as the front contact, and the whole top surface is covered with an anti-reflection coating and toughened glass to maximise the light reaching the junction.

Step 3. When sunlight (photons) is absorbed near the junction, it generates electron-hole pairs exactly as in a photodiode; the junction's OWN built-in electric field (no external bias needed) then separates them, sweeping electrons towards the n-type silicon (collected at the front contact) and holes towards the p-type silicon (collected at the back contact).

Step 4. This charge separation develops a potential difference across the cell's terminals; connecting an external load lets a photocurrent flow through it. Many individual cells are wired in series/parallel into a solar panel/module, and many panels together form a solar array for higher-power use. …

Explain the photovoltaic charge-separation mechanism at the p-n jun …

• Confusing the solar cell's principle (photovoltaic effect, no bias needed) with the photodiode's (reverse bias needed). …