104
I. Osaka
to high crystallinity with close π–π stacking distances. The polymers, benefited
from higher crystalline structure, showed high charge carrier mobilities as high as
0.4 cm
2 V
−1 s
−1 in OFET devices. Importantly, it was found that the backbone
orientation, i.e., edge-on and face-on, was altered by the composition of the side
chain length and topology. The difference in the orientation critically impacted the
photovoltaic performance, in particular, at the thick active layer in the conventional
cell, though in all polymers the orientation motif turned to the face-on in the blend
film. The FF gently decreased with the increase in the active layer thickness for the
polymers with face-on orientation, while the J SC increased, resulting in the higher
PCE. On the other hand, the FF decreased more significantly for the polymers with
edge-on orientation, giving rise to the lower PCE. However, this was not the case in
the inverted cell. Both the edge-on-polymers and face-on-polymers showed similar
dependence in the photovoltaic performance by the active layer thickness, where the
FF gently decreased with increasing thickness. We found that, interestingly, there
is a clear difference in the distribution of the backbone orientation through the film
thickness between the edge-on-polymers and face-on-polymers in the blend film,
which seemingly correlated well with the difference in the thickness dependence in
the photovoltaic performance.
5.3 Naphthobischalcogenadiazole-Based Polymers
5.3.1 Naphthobischalcogenadiazoles
Among the many acceptor building units, benzochalcogenadiazoles (BXz) such as
2,1,3-benzoxadiazole (BOz) [31], 2,1,3-benzothiadiazole (BTz) [14], and 2,1,3benzoselenadiazole (BSz) [32] (Fig. 5.14) including their derivatives have been
widely investigated and have afforded a large number of π-conjugated polymers
that show great performances in polymer solar cells. As their doubly fused system,
Fig. 5.14 Chemical
structures of
a benzochalcogenadiazoles
and b naphthobischalcogenadiazoles
I. Osaka
to high crystallinity with close π–π stacking distances. The polymers, benefited
from higher crystalline structure, showed high charge carrier mobilities as high as
0.4 cm
2 V
−1 s
−1 in OFET devices. Importantly, it was found that the backbone
orientation, i.e., edge-on and face-on, was altered by the composition of the side
chain length and topology. The difference in the orientation critically impacted the
photovoltaic performance, in particular, at the thick active layer in the conventional
cell, though in all polymers the orientation motif turned to the face-on in the blend
film. The FF gently decreased with the increase in the active layer thickness for the
polymers with face-on orientation, while the J SC increased, resulting in the higher
PCE. On the other hand, the FF decreased more significantly for the polymers with
edge-on orientation, giving rise to the lower PCE. However, this was not the case in
the inverted cell. Both the edge-on-polymers and face-on-polymers showed similar
dependence in the photovoltaic performance by the active layer thickness, where the
FF gently decreased with increasing thickness. We found that, interestingly, there
is a clear difference in the distribution of the backbone orientation through the film
thickness between the edge-on-polymers and face-on-polymers in the blend film,
which seemingly correlated well with the difference in the thickness dependence in
the photovoltaic performance.
5.3 Naphthobischalcogenadiazole-Based Polymers
5.3.1 Naphthobischalcogenadiazoles
Among the many acceptor building units, benzochalcogenadiazoles (BXz) such as
2,1,3-benzoxadiazole (BOz) [31], 2,1,3-benzothiadiazole (BTz) [14], and 2,1,3benzoselenadiazole (BSz) [32] (Fig. 5.14) including their derivatives have been
widely investigated and have afforded a large number of π-conjugated polymers
that show great performances in polymer solar cells. As their doubly fused system,
Fig. 5.14 Chemical
structures of
a benzochalcogenadiazoles
and b naphthobischalcogenadiazoles