RIKEN Accel. Prog. Rep. 48 (2015)

Ⅲ-2. Atomic & Solid State Physics (Muon)

Study of charge carrier transport in active layer P3HT:ZnO:PCBM hybridsolar cells measured by muon spin relaxation†
L. Safriani,*1 Risdiana,*1 A. Bahtiar,*1 A. Aprilia,*1 and I. Watanabe*2†

Condensed from the article submitted to Materials Science Forum
Department of Physics, Padjadjaran University＊2
RIKEN Nishina Center＊1P3HT:ZnO:PCBM at 15K

100 mT
50 mT

2020 mT
10 mT
5 mT
2 mT

10P3HT:ZnO:PCBM at 25K

30395 mT200 mT

100 mT
50 mT

2020 mT
10 mT
5 mT
2 mT

100 mT

00246Time (sec)

395 mT
200 mT

Asymmetry

Asymmetry

300 mT

0802468Time (sec)

Fig. 1. The asymmetry data of P3HT:ZnO:PCBM at 15 K
and 25 K for various longitudinal magnetic fields.
Figure 2 shows the LF dependence of 1 inP3HT:ZnO:PCBM, where 1 is the depolarization rate
associated with the fast component. At 15K, the relationship ~ H-0.5 is observed clearly, which indicate that onedimensional intra-chain diffusion occurs in this system.
Compared with the SR data for P3HT that show adimensional crossover at 25K,3) the data for
P3HT:ZnO:PCBM show the dimensional crossover fromone-dimensional to three-dimensional apparently at a lower
temperature. We cannot explain the experimental results
immediately, but they are likely related to the advantageous
properties of ZnO nanoparticles that facilitate electrontransfer.
101101P3HT:ZnO:PCBM
T = 15 K

100

P3HT:ZnO:PCBM
T = 25 K100

-1 (sec ) (sec-1)

Recently, many researchers have been making an effort toobtain high performance of solar cells by modifying theactive material of the solar cell. Conjugated polymers arepromising active materials. Much attention has been paid topolythiophene and its derivatives owing to their chemical
and thermal stability in addition to their potential to absorb
the solar spectrum in solar cells. Poly(3-hexylthiophene)(P3HT), a derivative of poly(3-alkylthiophene), presents thehighest hole mobility,1) thus attracting researchers’attention.
Hybrid solar cells that combine organic and inorganic
materials have been developed to increase the performanceof solar cells. P3HT having the highest hole mobility, whencombined with inorganic materials with the highest electronmobility, shows promise for better performance. Zinc oxide(ZnO) is an inorganic material that has high electron
mobility and is easy to prepare. In bulk heterojunction
systems of solar cells, ZnO behaves as an electron acceptor
to dissociate excitons formed in P3HT. For practicalapplication to solar cells, ZnO nanoparticles are prepared toresolve the problem associated with the small diffusion
range of P3HT.2) Fullerene and its derivative [6,6]-phenyl
C61 butyric acid methyl ester (PCBM) are well-known
acceptor materials for polymer solar cells owing to theirability to transfer excitons from polymers within 45 fs.3)
In previous studies, ZF- and longitudinal-field (LF)-μSR
measurements were performed on samples of P3HT4) andP3HT:ZnO.5) For both the samples, it was found that charge
carrier transport changes from intra-chain to inter-chain
diffusion. For P3HT:ZnO, one-dimensional intra-chain
diffusion was observed at low temperatures, while
three-dimensional inter-chain diffusion was observed athigh temperatures.5) The addition of PCBM into theP3HT:ZnO blend increased the charge transfer from P3HTto ZnO and also reduced the aggregation of ZnO
nanoparticles.
To clarify the charge carrier dynamics in a bulk ternary
system of hybrid materials, we measured charge carriertransport using LF-SR in the P3HT:ZnO blend by adding afullerene derivative (PCBM).
Figure 1 shows the LF dependence of the raw asymmetryat 15 K and 25 K. The initial asymmetry increases withincreasing LF field owing to the repolarization of themuonium state.6) The raw asymmetries at 15 K and 25 K
show a clear dependence on field and temperature.

10-1
10-2

10-1
10-2
10-3

10-3
0

1010

1

HLF (mT)

102

10

3

100

101

HLF (mT)

102

103

Fig. 2. The longitudinal-field dependence of the relaxation
rate 1 of P3HT:ZnO:PCBM at 15 K and 25 K.
With increasing temperature, the charge carrier transfer
changes from intra-chain to inter-chain diffusion.
One-dimensional intra-chain diffusion is observed in thesamples
attemperatures
below
15K,
while
three-dimensional inter-chain diffusion is observed attemperatures above 25 K.
References
1)
2)
3)
4)

W. Ma et al.: Adv. Funct. Mater. 15, 1617-1622 (2005)
L. W. Ji et al.: J Matter Sci. 45, 3266-3269 (2010)
G. Zerza et al.: Synth. Metals 119, 637 (2001)
R. Risdiana, et al.: Journal of Physics Conf. Series 200,052024-052027 (2010)5) L. Safriani et al.: Adv. Mater. Res. 896, 477-480 (2014)6) F. L. Pratt: Philos.Mag. Lett. 75, 371-380 (1997)- 272 -完全版2014_本文.indd 272

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