62
M. Hiramoto
3.4.1.6 Active Area of Lateral Cell
Notably, in the lateral cell, the active area for generating photocurrent was only
near the right-hand edge of the hole collection electrode (Fig. 3.12b). The maximum
photocurrent density obtained for the lateral cell was comparable to that for the
vertical reference cell (Fig. 3.12b, L = 0 μm). The shape of J-V curve for vertical
reference cell (Fig. 3.14a, broken black curve E) coincided well with that for the
lateral type cell (Fig. 3.14a, orange curve A). This strongly suggests that the photocurrent density of lateral-type cell (L = 20 μm) reached that of vertical reference cell (L
= 0 μm). Based on this comparison, we could calculate the width of the active area
as 8 μm for generating a photocurrent near the right-hand edge of the hole collection
electrode (Fig. 3.12b).
3.4.1.7 Possibility of Millimeter Carrier Range
Based on Eq. (3.1), the electron lifetime τ e was calculated to be 0.52 ms using L e =
30 μm. Here, the electron mobility μ e of the NTCDA single crystal was determined
to be 2.9 × 10
−2 cm
2 ·V
−1 ·s
−1 from the field-effect transistor measurement, and the
built-in field for the lateral cell with L = 30 μm was used for the value of E (2 × 10
2
V·cm
−1 ). The value of τ e obtained (0.52 ms) is of the order of milliseconds, which
would enable L e to be of the order of millimeters if single-crystal organic materials
with the μ e of 1 cm
2 ·V
−1 ·s
−1 were used. There is a strong probability of achieving
millimeter-order L e because an electron mobility of 1.7 cm
2 ·V
−1 ·s
−1 has already
been reported for a perylene derivative [22].
3.4.2 Lateral Junctions
In this section, a lateral alternating multilayered junction using a high-mobility crystalline organic semiconductor is proposed and demonstrated [23]. Essentially, the
photogenerated holes and electrons are laterally transported and extracted to the
respective electrodes. A total of 93% of the photogenerated electrons and holes
were laterally collected over a millimeter-scale distance of 0.14 mm. The excitoncollection efficiency reached 75% in a lateral alternating multilayered junction with
a layer thickness of 10 nm. Therefore, a lateral organic alternating multilayered
junction that completely collects both excitons and carriers could be an alternative
blended junction for organic solar cells.
3.4.2.1 Concept
Figure 3.15a shows the concept of a lateral alternating multilayered junction cell
consisting of hole pathways (Fig. 3.15b) and electron pathways (Fig. 3.15c), which
M. Hiramoto
3.4.1.6 Active Area of Lateral Cell
Notably, in the lateral cell, the active area for generating photocurrent was only
near the right-hand edge of the hole collection electrode (Fig. 3.12b). The maximum
photocurrent density obtained for the lateral cell was comparable to that for the
vertical reference cell (Fig. 3.12b, L = 0 μm). The shape of J-V curve for vertical
reference cell (Fig. 3.14a, broken black curve E) coincided well with that for the
lateral type cell (Fig. 3.14a, orange curve A). This strongly suggests that the photocurrent density of lateral-type cell (L = 20 μm) reached that of vertical reference cell (L
= 0 μm). Based on this comparison, we could calculate the width of the active area
as 8 μm for generating a photocurrent near the right-hand edge of the hole collection
electrode (Fig. 3.12b).
3.4.1.7 Possibility of Millimeter Carrier Range
Based on Eq. (3.1), the electron lifetime τ e was calculated to be 0.52 ms using L e =
30 μm. Here, the electron mobility μ e of the NTCDA single crystal was determined
to be 2.9 × 10
−2 cm
2 ·V
−1 ·s
−1 from the field-effect transistor measurement, and the
built-in field for the lateral cell with L = 30 μm was used for the value of E (2 × 10
2
V·cm
−1 ). The value of τ e obtained (0.52 ms) is of the order of milliseconds, which
would enable L e to be of the order of millimeters if single-crystal organic materials
with the μ e of 1 cm
2 ·V
−1 ·s
−1 were used. There is a strong probability of achieving
millimeter-order L e because an electron mobility of 1.7 cm
2 ·V
−1 ·s
−1 has already
been reported for a perylene derivative [22].
3.4.2 Lateral Junctions
In this section, a lateral alternating multilayered junction using a high-mobility crystalline organic semiconductor is proposed and demonstrated [23]. Essentially, the
photogenerated holes and electrons are laterally transported and extracted to the
respective electrodes. A total of 93% of the photogenerated electrons and holes
were laterally collected over a millimeter-scale distance of 0.14 mm. The excitoncollection efficiency reached 75% in a lateral alternating multilayered junction with
a layer thickness of 10 nm. Therefore, a lateral organic alternating multilayered
junction that completely collects both excitons and carriers could be an alternative
blended junction for organic solar cells.
3.4.2.1 Concept
Figure 3.15a shows the concept of a lateral alternating multilayered junction cell
consisting of hole pathways (Fig. 3.15b) and electron pathways (Fig. 3.15c), which