It is possible to divide light into many wavelengths. The light that affects the cell contains photons consisting of a large variety of energies. Not all of them have energy enough to modify the opening-electron pair. However, there are other electrons that contain lots of energy. Only a specific portion of this energy, measured in terms of eV or electron volts is necessary to knock an extra electron loose. This is commonly known as a material’s band gap energy. If a photon contains excess energy than what is required, the additional energy gets lost. However, if the incremental energy is equal to the required amount, there is possibility of the formation of more than one electron – hole couple. But, the latter effect does not seem to be of much significance. Just these two outcomes account for more than 70 percent loss of the incident concerning radiation energy on the cell.
There are more losses involved in the process. The electrons need to drift from one side to another of the cell using an outer circuit. The bottom can be covered using a metal, leading to effective conduction. But in case the top is completely covered, the photons are unable to pass through the opaque conductor and lose most of their current.
In order to reduce these losses, cells are normally covered using a contact grid made of metal that lessens the distance required to travel by the electrons, covering just a limited part of the surface of the cell. Even then, the grid blocks a few electrons.