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

Quantum 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 (ΔφF) which is directly linked to the radiative losses. For the first time we have successfully measured ΔφF 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) ΔφF is not the same in both wells which contradicts the assumption made by some researchers. (3) ΔφF shows a dependence on the separation between the two QWs at low temperatures.