Describe the construction, working, and use of a solar cell.

(N/A) solar cell is essentially a $p-n$ junction that generates an electromotive force $(emf)$ when solar radiation falls on the junction. Sunlight is not strictly required; any light with photon energy greater than the band gap energy $(E_{g})$ of the semiconductor can produce a photovoltage. The working principle of a solar cell is based on the photovoltaic effect, similar to a photodiode, but it does not require an external bias voltage.
Construction:
$1$. $A$ $p-Si$ wafer of about $300 \mu m$ thickness is taken.
$2$. $A$ thin layer $(\, 0.3 \mu m)$ of $n-Si$ is grown on one side by a diffusion process to form a $p-n$ junction.
$3$. The bottom of the $p-Si$ wafer is coated with a metal to form the back contact.
$4$. On the top of the $n-Si$ layer, a metallic grid (or finger electrode) is deposited to serve as the front contact. This grid covers only a small fraction of the area $( < 15 \%)$ to allow maximum light incidence.
Working:
The generation of $emf$ occurs through three basic processes:
$(1)$ Generation of electron-hole $(e-h)$ pairs due to light absorption $(h\nu > E_{g})$ near the junction.
$(2)$ Separation of electrons and holes due to the electric field of the depletion region. Electrons are swept to the $n$-side and holes to the $p$-side.
$(3)$ Collection of charges: Electrons reaching the $n$-side are collected by the front contact, and holes reaching the $p$-side are collected by the back contact. This makes the $p$-side positive and the $n$-side negative, creating a photovoltage.
Use:
Solar cells are used in calculators, watches, satellites, and for power generation in remote areas.