This work illustrates the effect of nano-antenna shape on the efficiency of a complete nano-rectenna system for one specific geometry: the bowtie. The bowtie geometry is very well known for its wider band characteristics compared to the straight dipole. Based on full wave electromagnetic field solvers, the radiation efficiency and maximum matching efficiency for nano-bowties with different lengths and base angles are calculated. The results demonstrate that by adopting the bowtie topology, the radiation efficiency for an aluminum dipole can be improved from 51% to 61%, while the relative total efficiency can be improved from 46% to 57%, compared to the common straight nano-dipole mainly used in literature.