  In this study, we investigate the morphological, structural, and optical
properties of both bulk-heterojunction and composite nanotubes that composed of
thiophene-based small molecules BHBT2 and fullerene PC71BM. Mix-blended and
template-assisted methods were used to fabricate the bulk-heterojunction and
composite nanotubes, respectively. A single material of BHBT2 thin films and
nanotubes that fabricated via spin-coating and template-assisted methods,
respectively, was also studied. Two different formations between
bulk-heterojunction and composite nanotubes were compared to elaborate their
advancement in properties. Absorption spectra of BHBT2:PC71BM
bulk-heterojunction and composite nanotubes have fallen within the
ultraviolet-visible (UV-vis) range. Field emission scanning electron microscope
(FESEM) and high-resolution transmission electron microscope (HRTEM) images
show that the carbon-rich of PC71BM, has successfully infiltrated into the
BHBT2 nanotube to form the BHBT2:PC71BM composite nanotubes. However, due to
the informality distribution of infiltration, charge carrier transfer is seen
to be better in bulk-heterojunction rather than in the composite nanotubes.
