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

RIKEN Accel. Prog. Rep. 51 (2018)

Eﬀect of light irradiation on charge carrier dynamics in active layer
hybrid solar cells
L. Safriani,∗1 Risdiana,∗1 Fitrilawati,∗1 A. Bahtiar,∗1 A. Aprilia,∗1 D. Puspita Sari,∗2 J. Angel,∗2
and I. Watanabe∗2∗1∗2Department of Physics, Padjadjdaran University
RIKEN Nishina Center

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10Fig. 1. The asymmetry data of P3HT:ZnO at 10, 15, 25, and
300 K for various longitudinal magnetic field values.
15 K

10 K

300 K

25 K

100

100

λ μ

Solar power generation is a key method for generating
electronic power. Several researchers have attempted toachieve higher performance of the solar cells and more
eﬀective materials for use in cells. The discovery ofconjugated polymers, such as Polythiophene (PT) and
its derivatives, attracted much attention owing to theirchemical and thermal stability as well as their potential
use as an absorbing solar spectrum material (active layer)
in solar cells. The most necessary property of these active layers is their ability to transfer the charge carrier
resulting from the absorption of solar spectrum. In particular, Poly(3-hexylthiophene)/P3HT has considerable
research interest, because it shows the highest hole mobility among the series of Poly(3-alkylthiophene).1) In ourprevious muon Spin Relaxation (µSR) study, the charge
carrier mobility in P3HT was found to change fromone-dimensional to a three-dimensional model, which isstrongly dependent on their molecular structure and temperature.2,3)
Recently, the so-called hybrid (organic-inorganic) solar cell was developed owing to the combined advantage
between organic material (P3HT) and inorganic material such as ZnO, which ensures better performance forpractical application. ZnO is inorganic material withhigh electron mobility and can be easily prepared as electron acceptor to dissociate excitons formed in conjugatedpolymer as the active material of solar cells. ZnO can beprepared as a nanoparticle that can resolve the problemof small diﬀusion range of P3HT.4) The existence of ZnOin active layer will support charge transfer from P3HT
to electrode of solar cell because the conduction bandof ZnO is lower than that of low unoccupied molecularorbital (LUMO) of P3HT.
We studied the microscopic intrinsic charge carrier dynamics in active material of P3HT:ZnO along and perpendicular to the chain by using the longitudinal ﬁeld(LF) µSR method. We found that the charge carrier
mobility changes from intrachain to interchain diﬀusion
above 25 K for P3HT:ZnO. We also have measured charge
carrier dynamics of P3HT:ZnO with light irradiation.
Figure 1 shows the asymmetry data of P3HT:ZnO at 10,
15, 25, and 300 K for various longitudinal magnetic ﬁeldvalues with (red data) and without (black data) light irradiation. We found small changes of asymmetry whenlight irradiation on condition and oﬀ condition, however
we cannot observe signiﬁcant eﬀect probably due to low
intensity of light irradiation.
Figure 2 show the longitudinal-ﬁeld dependence of relaxation rate λ1 of P3HT:ZnO nanoparticles at 10, 15,25, and 300 K. Without light irradiation, for the low-100

100

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10-1
100

101

102

103

10-1
100

101

102

103

10-1100 

101

102

103

10-1100

101

102

103

Fig. 2. The longitudinal-field HLF dependence of relaxation
rate λ1 of P3HT:ZnO nanoparticles at 10, 15, 25, and300 K.

est temperature of 10 K, λ ∼ H −0.5 is clearly displayedindicating one-dimensional intra-chain diﬀusion. In contrast, for the same temperature, light irradiation displayed λ ∼ C − H 0.5 curve, indicating three-dimensional
inter-chain diﬀusion. Thus, it is clearly seen that withlight irradiation, temperature crossover occurred fromone-dimensional to three-dimensional at the lower temperature of 10 K compared to that in a previous resultat 25 K.5)
References
1) A. Babel et al., Synth. Met. 148, 169 (2005).
2) Risdiana et al., Journal of Physics Conf. Series 200, 052024(2010).
3) Risdiana et al., Physica B 405, S381 (2010).
4) L. W. Ji et al., J. Matter Sci. 45, 3266 (2010).
5) L. Safriani et al., AMR 896, 477 (2014).

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