Downconversion

The application of downconversion as a way to increase the energy conversion efficiency of low threshold solar cells is reviewed. The theory of downconversion as applied to photovoltaic devices is revised from a thermodynamical standpoint. Various scenarios are analyzed, corresponding to downconverting and carrier multiplication devices. It is shown that downconversion can proceed from a state with less than twice the energy of the emitted photons, due to the entropically favorable nature of the exciton fission process. Both approaches comprising the state-of-the-art technology are described—downconversion using rare-earth ions and singlet fission in organic molecules and semiconductor nanostructures.