Question

Write a short note on (a) Photodiode; (b) Photovoltaic cell

Short answer

(a) A photodiode converts light into an electrical current and detects light. (b) A photovoltaic cell converts sunlight directly into electrical energy.

Step-by-step solution

Understanding Photodiode

A photodiode is a semiconductor device that converts light into an electrical current. It operates by absorbing photons and generating electron-hole pairs, resulting in a current. Photodiodes are commonly used in light detection, medical instruments, and optical communication systems.

Working of Photodiode

When light falls on the photodiode, it generates a photocurrent proportional to the intensity of the incident light. This current flows through an external circuit and can be measured. The photodiode is often operated in reverse bias to enhance sensitivity and response speed.

Understanding Photovoltaic Cell

A photovoltaic cell, commonly known as a solar cell, converts sunlight directly into electrical energy through the photovoltaic effect. This device consists mainly of semiconductor materials, typically silicon, which generate a voltage and current when exposed to light.

Working of Photovoltaic Cell

When light hits the photovoltaic cell, it excites electrons, causing them to jump from the valence band to the conduction band, creating electron-hole pairs. These electrons and holes are separated by the electric field within the cell, generating a flow of electric current that can be harnessed for power.

Key concepts

Semiconductor Device

A semiconductor device is a material with electrical conductivity between that of a conductor and an insulator. Silicon is the most used semiconductor material. In photodiodes and photovoltaic cells, semiconductors are vital. They enable the conversion of light into electrical signals. Semiconductors have unique properties
that make them suitable for controlling electrical currents.

Light to Electrical Current

The core function of both photodiodes and photovoltaic cells is to convert light into electrical current. This happens because of their semiconductor materials. When light strikes these devices, it excites electrons, freeing them to move and create a flow of electricity.
This principle is applied in many fields:

• light detection
• solar energy
• communications
• medical devices

Photovoltaic Effect

The photovoltaic effect is the process through which light energy is converted into electrical energy. When photons hit a semiconductor material, they transfer their energy to electrons. These electrons are then excited to higher energy states, known as the conduction band. This leaves behind holes in the valence band.

In photovoltaic cells, the electric field helps to separate electrons and holes, creating an electric current. The result is the efficient conversion of sunlight into a usable electrical current. This effect is the basis for solar power technology.

Electric Current Generation

Generating electric current with photodiodes and photovoltaic cells involves creating and controlling electron flow. For photodiodes, light creates a small current used for detection purposes. In photovoltaic cells, sunlight produces a more substantial current for power generation.

• In a photodiode, the current measures light intensity.
• In a photovoltaic cell, the current is harnessed and used as a power source.

By understanding these principles, we can better appreciate how light can be transformed into electrical energy for various applications.