Question

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Present various types of solar cells You can use the following references: Semiconductor Physics and Devices, Chapter 14 Solar Cells

Answer 1

Solar cell and its working

A solar cell is an electronic device that converts an optical input into current. A solar cell is an example of a photovoltaic device. It works on the principle of photovoltaic effect. A photovoltaic device basically means the device will generate voltage when exposed to light and photovoltaic effect means it will convert light energy to electrical energy.

Light shining on the solar cell produces both a current and a voltage to generate electric power. This process requires -

• A material in which the absorption of light raises an electron to a higher energy state.
• The movement of this higher energy electron from the solar cell into an external circuit. The electron then dissipates its energy in the external circuit and returns to the solar cell.

Types of solar cells and application

Solar cells are typically named after the semiconducting material they are made of. These materials must have certain characteristics in order to absorb sunlight. Solar cells can be made of only one single layer of light absorbing material(single-junction) or use multiple physical configurations (multi-junctions) to take advantage of various absorption and charge seperation mechanisms.

Solar cells can be classified into - first, second and third generation cells.

• The first generation cells also called conventional, traditional or wafer-based cells are made of crystalline silicon, the commercially predominant PV technology, that includes materials such as polysilicon and monocrystalline silicon.
• Second generation cells are thin film solar cells, that include amorphous silicon, CdTe and CIGS cells and are commercially significant in utility-scale photovoltaic power stations, building integrated photovoltaic or in small stand alone power system.
• The third generation of solar cells includes a number of thin-film technologies often described as emerging photovoltaics Most of them have not yet been commercially applied and are still in the research or development phase.

"First generation" panels include silicon solar cells. They are made from a single silicon crystal(mono-crystalline), or cut from a block of silicon that is made up of many crystals(multi-crystalline).

"Second generation" thin film solar cells are less expensive to produce than traditional silicon solar cells as they require a decreased amount of materials for construction. The thin-film PV cells are, just as the name implies, a physically thin technology that has been applied to photovoltaics. They are only slightly less efficient than other types but do require more surface area to generate the same amount of power.

Brief discussion of some typical solar cells

Amorphous silicon solar cell (A-Si)

• Non-crystalline form of silicon
• Most well developed of the thin film technologies that have been on the market for more than 15 years.
• Widely used in pocket calculators. It also powers some private homes, buildings and remote facilities.
• In its simplest form, its cell structure has a single sequence of p-i-n layers.
• There is only very short range order and no crystalline regions are observed.