Chemical structures of (a) head-to-tail RR-P3HT, (b) head-to-head , and (c) PCBM. The principal axes of factor and proton hyperfine coupling of electrons are also shown in (a).
First-derivative ESR signals of the RR-P3HT/PCBM composite obtained under the dark condition (dashed curve) and under illumination (solid curve) at 60 K. The PCBM concentration is 5 mol %. The definitions of the value and linewidth are also given. Inset shows the transient response of the LESR intensity upon the light illumination.
Excitation power dependence of the prompt LESR intensity obtained for the RR-P3HT/PCBM composites with different PCBM concentrations at 60 K; 5 mol % (diamonds), 36 mol % (triangles), and 55 mol % (rectangles). The solid line shows the fitting by the QR model of dependence. The dashed lines show the dependence expected for the BR model.
Decay curve of the normalized peak intensity after turning off the excitation light in the RR-P3HT/PCBM (5 mol %) composite at 60 K. The excitation light power is . The solid curve represents the fitting curve by Eq. (3). The dashed curve represents the one by BR model expressed as . The inset shows a double logarithmic plot of vs time at 60 K.
Temperature dependence of obtained for as-grown samples of RR-P3HT/PCBM composites with various PCBM concentrations; 5 mol % (diamonds), 18 mol % (circles), 36 mol % (triangles), and 55 mol % (rectangles). The dashed lines show the fitting of the data in the hopping region by the activation-type formula.
Temperature dependence of obtained for the RR-P3HT/PCBM (55 mol %) composite. The open and solid circles correspond to the data obtained for the as-grown sample and for the sample after annealing at for 10 min, respectively. The dashed lines show the fitting of the data in the hopping region by the activation-type formula.
Schematic illustration of the QR process. The shaded rectangles represent RR-P3AT molecules, which form the lamellar structure, as reported in Ref. 24. The solid arrows on the molecules represent the spins associated with the positive polaron on the polymer chain and the PCBM radical anions. If the two polarons approach each other, formation of the bipolaron or polaron pair with a charge of is expected. These states cause a stronger Coulomb attraction with the unpaired electrons on the PCBM radical anions (dashed arrows), resulting in a simultaneous recombination of QR type.
(a) Angular dependence of the value and ESR linewidth obtained in the RR-P3HT/PCBM (55 mol %) composite at 60 K. The circles show the values and the triangles the linewidths. The open and solid symbols correspond to the results obtained before and after annealing, respectively. denotes the angle between the applied magnetic field and the substrate normal. (b) and (c) represent the PCBM concentration dependences of the anisotropy of the values and linewidth, respectively, which are defined by the difference of the values observed with the magnetic field parallel and perpendicular to the substrate. The symbols are used by the same definition with (a).
Absorption spectra of the RR-P3HT/PCBM (36 mol %) composite film. The dashed and solid curves represent the data obtained before and after annealing, respectively.
First-derivative ESR signal of the composite (5 mol %) obtained under the dark condition (dashed curve) and under illumination (solid curve) at 60 K. Inset shows the time response of the LESR intensity upon the light illumination.
Excitation power dependence of the LESR intensity of the prompt component of obtained at 60 K. The dotted line represents the dependence of BR process, while the dashed line represents the dependence of QR process. The solid curve represents the fitting curve by Eq. (2) considering both QR and BR processes.
Decay curve of the normalized peak intensity after turning off the excitation light obtained for composite at 60 K. The excitation power is . The solid curve shows the fitting by Eq. (3). Inset shows the temperature dependence of obtained for composite. Dashed line represents the fitting by the activation-type formula in the hopping region.
Activation energies and the QR rate constant at 100 K (hopping regime) and that at 60 K (tunneling regime) obtained for the RR-P3HT/PCBM composites with various PCBM mixing ratios.
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