Band Gap Solar Panels

Band gap energy differs from one material to another.

Band gap solar panels.

The optical band gap see below determines what portion of the solar spectrum a photovoltaic cell absorbs. The band gap determines how much energy is needed from the sun for conduction as well as how much energy is generated. In the bond model of a semiconductor band gap reduction in the bond energy also reduces the band gap. This maximum occurs at a band gap of 1 34 ev.

Limiting efficiency of solar cells solar cells operate on. Therefore increasing the temperature reduces the band gap. 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. 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.

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. A semiconductor will not absorb photons of energy less than the band gap. It has been estimated that about 1 1 loss occurs for every 1 c rise in temperature of the cell. Actually the energy converted is the energy corresponding to the band gap.

The actual band gap for formamidinium fa lead trihalide can be tuned as low as 1 48 ev which is closer to the ideal bandgap energy of 1 34 ev for maximum power conversion efficiency single junction solar cells predicted by the shockley queisser limit. In a solar cell the parameter most affected by an increase in temperature is the open circuit voltage. And the energy of the electron hole pair produced by a photon is equal to the bandgap energy. Photons with more energy than necessary to separate an electron pair do generate an electron and a hole with the balance of their enegy being dissipated in the form of heat.

Photons with energy less than the band gap will not separate electron pairs and simply pass through the solar cell. So the result is a loss in efficiency. 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. Rest of the photon energy is simply a waste in the solar cell as heat.