  The GaAs/AlGaAs quantum well solar cell (QWSC) shows promise as a novel
approach to higher efficiency solar cells but suffers from a poor short circuit
current Jsc. We report on efforts to reduce this problem with the use of
compositional grading and back surface mirroring. We present experimental
quantum efficiency (QE) data on a range of compositionally graded QWSCs and
devices in which the back surface of the cell is coated with a mirror,
increasing the optical thickness of the quantum well layer in the long
wavelength range. The experimental QE spectra are reproduced by a model which
deals with arbitrary compositional profiles and optical cavities formed in the
mirrored cells. The model is used to design an optimised QWSC, and projected
Jsc values given. Applications including II-VI and tandem solar cells are
considered.
