  We theoretically investigate the thermoelectric properties of zigzag graphene
nanoribbons in the presence of extended line defects, substrate impurities and
edge roughness along the nanoribbon's length. A nearest-neighbor tight-binding
model for the electronic structure and a fourth nearest- neighbor force
constant model for the phonon bandstructure are used. For transport we employ
quantum mechanical non-equilibrium Green's function simulations. Starting from
the pristine zigzag nanoribbon structure that exhibits very poor thermoelectric
performance, we demonstrate how after a series of engineering design steps the
performance can be largely enhanced. Our results could be useful in the design
of highly efficient nanostructured graphene nanoribbon based thermoelectric
devices.
