Photovoltaic efficiency enhancement through thermal up-conversion

A scheme is presented whereby ambient thermal energy is coupled to sub-band-gap photons through the creation and recombination of electron hole pairs, thereby increasing the short-circuit current and the efficiency of a solar cell. The necessary photon-phonon coupling is demonstrated experimentally, through the observation of anti-Stokes luminescence from QW p-i-n devices. A modest efficiency enhancement is possible for a constrained PV device, but the maximum efficiency does not exceed that of the Shockley-Queisser limit. Only when a temperature difference between the PV device and QW thermal up-convertor is established, can the system exceed the Shockley-Queisser limit.