Control of the energetic structure of photovoltaic co-deposited films consisting of fullerene and α-sexithiophene was demonstrated by ppm-level doping with molybdenum oxide (MoO3). The transition from an n-type Schottky junction via a metal/insulator/metal junction to a p-type Schottky junction by increasing the MoO3 doping concentration was verified by observing the photovoltaic properties. Direct ppm-level doping into photoactive co-deposited films could become a powerful tool for designing the appropriate built-in potential for efficient organic photovoltaic cells.

1.
Organic Photovoltaics, Mechanisms, Materials and Devices
, edited by
S.-S.
Sun
and
N. S.
Sariciftci
(
CRC
,
New York
,
2005
).
2.
H.
Spanggaard
and
F. C.
Krebs
,
Sol. Energy Mater. Sol. Cells
83
,
125
(
2004
).
3.
H.
Hoppe
and
N. S.
Sariciftci
,
J. Mater. Res.
19
,
1924
(
2004
).
4.
C. W.
Tang
,
Appl. Phys. Lett.
48
,
183
(
1986
).
5.
M.
Hiramoto
,
H.
Fujiwara
, and
M.
Yokoyama
,
Appl. Phys. Lett.
58
,
1062
(
1991
).
6.
M.
Hiramoto
,
H.
Fujiwara
, and
M.
Yokoyama
,
J. Appl. Phys.
72
,
3781
(
1992
).
7.
K.
Suemori
,
T.
Miyata
,
M.
Yokoyama
, and
M.
Hiramoto
,
Appl. Phys. Lett.
86
,
063509
(
2005
).
8.
M.
Hiramoto
,
Y.
Kishigami
, and
M.
Yokoyama
,
Chem. Lett.
19
,
119
(
1990
).
9.
M.
Hiramoto
,
K.
Ihara
,
H.
Fukusumi
, and
M.
Yokoyama
,
J. Appl. Phys.
78
,
7153
(
1995
).
10.
K.
Walzer
,
B.
Maennig
,
M.
Pfeiffer
, and
K.
Leo
,
Chem. Rev.
107
,
1233
(
2007
).
11.
W. E.
Spear
and
P. E.
Lecomber
,
Solid State Commun.
17
,
1193
(
1975
).
12.
M.
Kubo
,
T.
Kaji
,
K.
Iketaki
, and
M.
Hiramoto
,
Appl. Phys. Lett.
98
,
073311
(
2011
).
13.
M.
Kubo
,
T.
Kaji
, and
M.
Hiramoto
, “pn-Homojunction formation in single fullerene films”, AIP Advances (to be published).
14.
J.
Sakai
,
T.
Taima
, and
K.
Saito
,
Organic Electronics
9
,
582
(
2008
).
15.
T.
Matsushima
,
Y.
Kinoshita
, and
H.
Murata
,
Appl. Phys. Lett.
91
,
253504
(
2007
).
16.
R. A.
Laudise
,
Ch.
Kloc
,
P. G.
Simpkins
, and
T.
Siegrist
,
J. Cryst. Growth
187
,
449
(
1998
).
17.
M.
Hiramoto
and
K.
Sakai
,
Mol. Cryst. Liq. Cryst.
491
,
284
(
2008
).
18.
M.
Hiramoto
,
Proc. SPIE
7052
,
70520H
(
2008
).
19.
Distances from the MoO3 source to QCM and to substrate were 9 and 18 cm, respectively. Tooling factor determined by surface profilometer was 0.25. Total-thickness signal from QCM vs. time relationship was monitored by PC display. For 70 ppm MoO3, though there was very slow cycling fluctuation (frequency: ∼300 s, amplitude: ∼0.05 nm) of signal, reproducible increase of baseline of 0.06 nm, which observed only during MoO3 evaporation, per prolonged timescale of 4300 s was observed (1.4 × 10−5 nm s−1).
20.
C.
Falkenberg
,
C.
Uhrich
,
S.
Olthof
,
B.
Maennig
,
M.
Riede
, and
K.
Leo
,
J. Appl. Phys.
104
,
034506
(
2008
).
21.
VB position of 6T in C60:6T co-deposited film (5.5 eV) was different to single 6T film (5.2 eV) presumably due to the existence of 6T single molecules or tiny 6T aggregates, which interacts with C60.
22.
When one assumes the phase separation of 6T and C60, the energetic structure of the bulk of a co-deposited layer such as 6T/C60/6T/C60 can be depicted based on the measured values of EFs for C60 and 6T single layers and for a C60:6T co-deposited layer. For the MoO3-doped p-type case, holes are suggested to be mainly transported through the 6T region.
23.
By increasing the doping concentration from 1100 to 4300 ppm, the shortest wavelength peak where absorbance exceeds 3 (300-400 nm) became the main component. Obviously, the depletion layer of the p-type Schottky junction shrunk with increasing doping concentration.
24.
H.
Ishii
,
K.
Sugiyama
,
E.
Ito
, and
K.
Seki
,
Adv. Mater.
11
,
605
(
1999
).
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