Atomically
Precise Graphene Nanoribbon Heterojunctions
for Excitonic Solar Cells
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Abstract
By
mixing pure precursor monomers and nitrogen-doped equivalents,
atomically sharp wiggle-edged heterojunctions can be obtained via
the combined action of Ullmann coupling followed by cyclodehydrogenation
[Cai et al., <i>Nat. Nanotechnol.</i> <b>2014</b>, <i>9</i>, 896]. We used first-principles density functional theory
and the many-body <i>GW</i> approach to establish the role
of doping (boron and nitrogen) in a variety of graphene nanowiggles
displaying a range of band gaps. The substitution of C atoms located
at the edges of the structures does not significantly affect the magnitude
of the band gaps, but leads to their relative upshift or downshift
depending on the dopant. This shift is found to vary quasi-linearly
as the concentration of dopant increases. Consequently, tunable type-II
staggered band alignments are formed in graphene nanowiggle heterojunctions.
We predict that these type-II heterojunctions can provide ultrathin
solar cells with power conversion efficiencies up to 22.0%