  We report on the influence of the quantum well thickness on the effective
band gap and conversion efficiency of In0.12Ga0.88N/GaN multiple quantum well
solar cells. The band-to-band transition can be redshifted from 395 to 474 nm
by increasing the well thickness from 1.3 to 5.4 nm, as demonstrated by
cathodoluminescence measurements. However, the redshift of the absorption edge
is much less pronounced in absorption: in thicker wells, transitions to higher
energy levels dominate. Besides, partial strain relaxation in thicker wells
leads to the formation of defects, hence degrading the overall solar cell
performance.
