  The quantum well solar cell (QWSC) has been proposed as a flexible means to
ensuring current matching for tandem cells. This paper explores the further
advantage afforded by the indication that QWSCs operate in the radiative limit
because radiative contribution to the dark current is seen to dominate in
experimental data at biases corresponding to operation under concentration. The
dark currents of QWSCs are analysed in terms of a light and dark current model.
The model calculates the spectral response (QE) from field bearing regions and
charge neutral layers and from the quantum wells by calculating the confined
densities of states and absorption coefficient, and solving transport equations
analytically. The total dark current is expressed as the sum of depletion layer
and charge neutral radiative and non radiative currents consistent with
parameter values extracted from QE fits to data. The depletion layer dark
current is a sum of Shockley-Read-Hall non radiative, and radiative
contributions. The charge neutral region contribution is expressed in terms of
the ideal Shockley radiative and non-radiative currents modified to include
surface recombination. This analysis shows that the QWSC is inherently subject
to the fundamental radiative efficiency limit at high currents where the
radiative dark current dominates, whereas good homojunction cells are well
described by the ideal Shockley picture where the limit is determined by
radiative and non radiative recombination in the charge neutral layers of the
cell.
