The observation of thermal photon gain in quantum well solar cells

Photon gain, which indicates the breakdown of the Principle of Detailed Balance, has been observed in radiatively dominated quantum well solar cells (QWSCs) at illumination levels consistent with around 200x concentration. Evidence comes from three types of experiment. The radiative dark-current extracted from a short-circuit current versus open circuit voltage plot becomes steeper than expected for radiative recombination. The photoluminescence and electro-luminescence spectra from the lowest exciton broaden as illumination increases. We report evidence demonstrating that photon gain results from hot-carrier recombination. Our results support the hypothesis that hot carriers are responsible for the reduced radiative recombination in QWSCs and the voltage enhancement observed in triple-junction QWSCs.