An experimental and numerical study of a-SiGe:H based solar cells with
a band gap graded i layer in the shape of a ''V'' is presented. The v
ariation of the location of the band gap minimum has a strong influenc
e on solar cell performance. Under air mass (AM) 1.5 illumination the
cells show a strong increase in open circuit voltage and a distinct de
crease in the fill factor when shifting the band gap minimum from the
front to the rear part of the i layer. Comparisons of experimental and
simulated data of the dark I/V behavior, the I/V curves under illumin
ation and the quantum efficiency allow insights into the transport and
recombination behavior within the solar cell. The simulations reveal
that the position,as well as the charge state of the defects and, unde
r illumination additionally the recharging behavior of the defect stat
es, determine the device characteristics. (C) 1998 American Institute
of Physics.