Solar cells and energy payback

In the 1990s, when silicon cells were twice as thick, efficiencies were much lower than today and lifetimes were shorter, it may well have cost more energy to make a cell than it could generate in a lifetime. In the meantime, the technology has progressed significantly, and the energy payback time, defined as the recovery time required for generating the energy spent for manufacturing of the respective technical energy systems, of a modern photovoltaic module is

Equivalent circuit of a solar cell

The equivalent circuit of a solar cell
/wiki/File:Photovoltaic_cell.svg">

The schematic symbol of a solar cell

To understand the electronic behavior of a solar cell, it is useful to create a model which is electrically equivalent, and is based on discrete electrical components whose behavior is well known. An ideal solar cell may be modelled by a

Thin films

The various thin-film technologies currently being developed reduce the amount (or mass) of light absorbing material required in creating a solar cell.

This can lead to reduced processing costs from that of bulk materials (in the case of silicon thin films) but also tends to reduce energy conversion efficiency (an average 7 to 10% efficiency), although many multi-layer thin films have efficiencies above those of bulk silicon wafers.

They have become popular compared to wafer silicon due to lower costs and advantages including flexibility, lighter weights, and ease of integration.

Cadmium telluride solar cell

A cadmium telluride solar cell is a solar cell based on cadmium telluride, an efficient light-absorbing material for thin-film cells. Compared to other thin-film materials, CdTe is easier to deposit and more suitable for large-scale production.
There has been much discussion of the toxicity of CdTe-based solar cells. The perception of the toxicity of CdTe is based on the toxicity of elemental cadmium, a heavy metal that is a

Quantum efficiency of Solar Cells

As described above, when a photon is absorbed by a solar cell it can produce a pair of free charge carriers, i.e. an electron-hole pair. One of the carriers (the minority carrier) may then be able to reach the p-n junction and contribute to the current produced by the solar cell; such a carrier is said to be collected. Alternatively, the carrier may give up its energy and once again become bound to an atom within the solar cell without

Light-absorbing materials

All solar cells require a light absorbing material contained within the cell structure to absorb photons and generate electrons via the photovoltaic effect. The materials used in solar cells tend to have the property of preferentially absorbing the wavelengths of solar light that reach the Earth surface. However, some solar cells are optimized for light absorption beyond Earth's atmosphere as well. Light absorbing materials can often be used in multiple physical configurations to take advantage of different light absorption and charge separation mechanisms.
Photovoltaic panels are normally made of either silicon or thin-film cells:
Many currently available solar cells are configured as

The p-n junction of Solar Cell

The most commonly known solar cell is configured as a large-area p-n junction made from silicon. As a simplification, one can imagine bringing a layer of n-type silicon into direct contact with a layer of p-type silicon. In practice, p-n junctions of silicon solar cells are not made in this way, but rather by diffusing an n-type dopant into one side of a p-type wafer (or vice versa).

If a piece of p-type silicon is placed in intimate contact with a piece of n-type silicon, then a diffusion of electrons occurs from the