  We describe a mathematical model for heterojunctions in semiconductors which
can be used, e.g., for modeling higher efficiency solar cells. The continuum
model involves well-known drift-diffusion equations posed away from the
interface. These are coupled with interface conditions with a nonhomogeneous
jump for the potential, and Robin-like interface conditions for carrier
transport. The interface conditions arise from approximating the interface
region by a lower-dimensional manifold. The data for the interface conditions
are calculated by a Density Functional Theory (DFT) model over a few atomic
layers comprising the interface region. We propose a domain decomposition
method (DDM) approach to decouple the continuum model on subdomains which is
implemented in every step of the Gummel iteration. We show results for
CIGS/CdS, Si/ZnS, and Si/GaAs heterojunctions.
