Temperature-dependent study of the radiative losses in double-quantum well solar cells

lQuantum well solar cells (QWSC) have been proposed as a way to achieve a higher efficiency than conventional homogeneous cells. A key quantity for understanding the potential of the QWSC is the spatial variation of the quasi-Fermi level separation (Delta phi (F)) which is directly linked to the radiative losses. For the first time we have successfully measured Delta phi (F) in asymmetric double QW (DQW) p-i-n diodes in the AlGaAs/GaAs system at temperatures between 200 and 295 K. We have made several significant observations: (1) radiative losses through the QW decrease with increasing temperature and are clearly below the detailed balance-based predictions at room temperature. (2) Delta phi (F) is not the same in both wells which contradicts the assumption made by some researchers. (3) Delta phi (F) shows a dependence on the separation between the two QWs at low temperatures. (C) 2001 Published by Elsevier Science B.V. All rights reserved.