An approach to downconversion solar cells

We describe an approach to solar downconversion in which a semiconductor is used for absorption, and substitutional rare earth ions are used for emission. The semiconductor would provide broad-band absorption, and the rare earth ions would provide emission of multiple photons by a cross relaxation process in a narrow wavelength band. The emitted photons are then absorbed by a solar cell formed from a low band gap semiconductor such as silicon. Er and Yb are suggested owing to strong emission at 980 nm which are useful when the down-converter is paired with silicon solar cells. The use of InGaN is proposed for the absorbing host semiconductor.