The electroluminescence (EL) of high-efficiency mono-cry stal line silicon solar cells is compared to that of polycrystalline ZnO/CdS/Cu(In,Ga)Se-2 heterojunction solar cells. Both types of devices exhibit a remarkable efficiency as light emitting diodes. The external quantum efficiency Q(LED) defined as the ratio between radiative and total recombination currents is QLED approximate to 0. 13% in case of the silicon cell and QLED approximate to 0.03% for the Cu(In,Ga)Se-2 device. The luminescent emission of Cu(In,Ga)Se-2 changes from a broadened donor-acceptor pair recombination at temperatures T < 140 K to band-to-band recombination for T > 200 K. The emission of the silicon cell is dominated by transverse optical phonon assisted hand-to-hand recombination in the entire temperature range 90 K <= T <= 300 K. The reciprocity between the external (photovoltaic) quantum efficiency Q(c) and the electroluminescent emission of both devices is fulfilled. (c) 2006 Elsevier B.V. All rights reserved.