The photovoltaic system is based on the ability of certain materials to convert light directly into electricity. Although the basic physical principle has been known for a long time, the technical development of solar cells is far from over, and further improvements can be expected in the future.
Semiconductors owe their name to the property to behave both like an electrical conductor and like a non-conductor. In a solar cell, the non-conductive material becomes a conductor because the electrons are released from the non-conductive crystal compound through the absorption of a photon. The kinetic energy that they absorb forms the electricity generated. The energy of the photon must lie in a material-dependent interval that is precisely limited. Photons with too much or too little energy do not contribute to the generation of electricity. "The energy of a photon is directly proportional to its frequency". Therefore, it means that the usable part of the light spectrum is limited.
The search for new materials to replace the silicon most commonly used today is intensively pursued worldwide. The focus is on two properties that these new materials should have. First, the usable part of the light spectrum should be as large as possible. Second, the so-called recombination rate should be as low as possible. It indicates how quickly the electrons spontaneously fall back from the conductive to the non-conductive state. The still low efficiency of organic photovoltaics is related to the fact that this recombination rate is comparatively high in organic semiconductors.