6 Charge Carrier Dynamics in Polymer Solar Cells
139
6.4.4 Ternary Blend Polymer Solar Cells
Figure 6.12 shows transient absorption spectra of RR-P3HT/PCBM binary and RRP3HT/PCBM/SiPc6 ternary blend films upon the laser excitation of the P3HT absorption at 400 nm. As described before, the large absorption band at around 1250 nm
is ascribed to polymer singlet excitons. The negative signals at around 500 nm are
ascribed to the GSB of P3HT. A broad depression is observed from 650 to 850 nm,
which is ascribed to stimulated emission from P3HT. At 100 ps, broad absorption
bands are observed from 650 to 1000 nm, which is ascribed to polymer polarons.
For the RR-P3HT/PCBM binary blends, polymer singlet excitons decay with a time
constant of 25 ps (85%) and 330 ps (15%). Polymer polarons are generated with
the same time constant of 25 ps. Thus, this is ascribed to the charge generation
following exciton diffusion. The longer and minor time constant is ascribed to the
lifetime of polymer singlet excitons. For the RR-P3HT/PCBM/SiPc6 ternary blends,
on the other hand, polymer singlet excitons decay with a time constant of 4 ps (50%)
and the same time constants observed for the binary blends. Polymer polarons are
generated with a time constant of 6 ps. This disagreement in the two time constants
suggests that polymer polarons are not generated directly from polymer singlet excitons. There should be an intermediate state. As shown in Fig. 6.12c, a small but sharp
Fig. 6.12 Transient
absorption spectra of
a RR-P3HT/PCBM and
b RR-P3HT/PCBM/SiPc6
blend films measured at 0
(black), 1 (red), 10, (blue),
and 100 (light green) ps after
the laser excitation. The
excitation wavelength and
intensity were 400 nm and
6 μJ cm −2 , respectively.
c Transient absorption
spectra of RR-P3HT/PCBM
(black line) and
RR-P3HT/PCBM/SiPc6 (red
line) blend films measured at
10 ps Adapted with the
permission from [13].
Copyright 2010 American
Chemical Society
-2
0
2
600
900
1200
-2
0
2
a)
b)
ΔmOD
600
700
800
-1
-0.5
0
0.5 c)
Wavelength / nm
139
6.4.4 Ternary Blend Polymer Solar Cells
Figure 6.12 shows transient absorption spectra of RR-P3HT/PCBM binary and RRP3HT/PCBM/SiPc6 ternary blend films upon the laser excitation of the P3HT absorption at 400 nm. As described before, the large absorption band at around 1250 nm
is ascribed to polymer singlet excitons. The negative signals at around 500 nm are
ascribed to the GSB of P3HT. A broad depression is observed from 650 to 850 nm,
which is ascribed to stimulated emission from P3HT. At 100 ps, broad absorption
bands are observed from 650 to 1000 nm, which is ascribed to polymer polarons.
For the RR-P3HT/PCBM binary blends, polymer singlet excitons decay with a time
constant of 25 ps (85%) and 330 ps (15%). Polymer polarons are generated with
the same time constant of 25 ps. Thus, this is ascribed to the charge generation
following exciton diffusion. The longer and minor time constant is ascribed to the
lifetime of polymer singlet excitons. For the RR-P3HT/PCBM/SiPc6 ternary blends,
on the other hand, polymer singlet excitons decay with a time constant of 4 ps (50%)
and the same time constants observed for the binary blends. Polymer polarons are
generated with a time constant of 6 ps. This disagreement in the two time constants
suggests that polymer polarons are not generated directly from polymer singlet excitons. There should be an intermediate state. As shown in Fig. 6.12c, a small but sharp
Fig. 6.12 Transient
absorption spectra of
a RR-P3HT/PCBM and
b RR-P3HT/PCBM/SiPc6
blend films measured at 0
(black), 1 (red), 10, (blue),
and 100 (light green) ps after
the laser excitation. The
excitation wavelength and
intensity were 400 nm and
6 μJ cm −2 , respectively.
c Transient absorption
spectra of RR-P3HT/PCBM
(black line) and
RR-P3HT/PCBM/SiPc6 (red
line) blend films measured at
10 ps Adapted with the
permission from [13].
Copyright 2010 American
Chemical Society
-2
0
2
600
900
1200
-2
0
2
a)
b)
ΔmOD
600
700
800
-1
-0.5
0
0.5 c)
Wavelength / nm