  Carrier selective (CS) silicon solar cells are increasingly explored using a
variety of different materials. However, the optimum properties of such CS
materials are not well understood. In this context, through detailed analytical
and numerical modeling, here we provide several interesting insights on the
efficiency tradeoff with CS material properties. First, we show that perfect
band alignment is a desirable feature only if the interface is devoid of any
trap states. Otherwise, a band offset of around 0.2eV-0.4eV provides sufficient
band bending to reduce the effect of interface recombination, thus improving
the performance. Surprisingly, the interface passivation quality for the
minority carrier extraction layer is found to be far less demanding than that
for the majority carrier extraction layer. Additionally, doping density and
dielectric constant of CS layers have a similar effect as band offset on solar
cell performance. Our results have obvious implications toward the selection of
appropriate materials as carrier selective layers and hence are of broad
interest to the community.
