  We theoretically analyze the thermoelectric properties of graphene quantum
dot arrays (GQDAs) with line- or surface-contacted metal electrodes. Such GQDAs
are realized as zigzag graphene nanoribbons (ZGNRs) with periodic vacancies.
Gaps and minibands are formed in these GQDAs, which can have metallic and
semiconducting phases. The electronic states of the first conduction (valence)
miniband with nonlinear dispersion may have long coherent lengths along the
zigzag edge direction. With line-contacted metal electrodes, the GQDAs have the
characteristics of serially coupled quantum dots (SCQDs) if the armchair edge
atoms of the ZGNRs are coupled to the electrodes. By contrast, the GQDAs have
the characteristics of parallel QDs if the zigzag edge atoms are coupled to the
electrodes. The maximum thermoelectric power factors of SCQDs with
line-contacted electrodes of Cu, Au, Pt, Pd, or Ti at room temperature were
similar or greater than $0.186~nW/K$; their figures of merit were greater than
three. GQDAs with line-contacted metal electrodes have much better
thermoelectric performance than surface contacted metal electrodes.
