Band Gap Solar Panels

A semiconductor will not absorb photons of energy less than the band gap.

Band gap solar panels.

The optical band gap see below determines what portion of the solar spectrum a photovoltaic cell absorbs. Actually the energy converted is the energy corresponding to the band gap. So the result is a loss in efficiency. This maximum occurs at a band gap of 1 34 ev.

Photons with energy less than the band gap will not separate electron pairs and simply pass through the solar cell. Lower energy is therefore needed to break the bond. Band gap energy differs from one material to another. The band gap is the minimum amount of energy required for an electron to break free of its bound state.

Traditional single junction cells with an optimal band gap for the solar spectrum have a maximum theoretical efficiency of 33 16 the shockley queisser limit. In the bond model of a semiconductor band gap reduction in the bond energy also reduces the band gap. When the band gap energy is met the electron is excited into a free state and can therefore participate in conduction. Solar cells with multiple band gap absorber materials improve efficiency by dividing the solar spectrum into smaller bins where the thermodynamic efficiency limit is higher for each bin.

Rest of the photon energy is simply a waste in the solar cell as heat. And the energy of the electron hole pair produced by a photon is equal to the bandgap energy. The most popular solar cell material silicon has a less favorable band gap of 1 1 ev resulting in a maximum efficiency of about 32. Therefore increasing the temperature reduces the band gap.

The band gap determines how much energy is needed from the sun for conduction as well as how much energy is generated. That is of all the power contained in sunlight about 1000 w m 2 falling on an ideal solar cell only 33 7 of that could ever be turned into electricity 337 w m 2. It has been estimated that about 1 1 loss occurs for every 1 c rise in temperature of the cell. In a solar cell the parameter most affected by an increase in temperature is the open circuit voltage.