An Effect of Molecular Motion on Carrier Formation in a Poly(3-hexylthiophene) Film

Abstract

Free carriers, polarons (P), in conjugated polymers play a key role in the performance of optoelectronic devices. Here, we present solid evidence that P can be predominantly generated from polaron pairs (PP) in a poly(3-hexylthiophene) (P3HT) film under zero electric field. P formation from PP strongly depends on temperature. The temperature dependence of P starts to change around 300 K. P3HT exhibits a thermal molecular motion named the α1 relaxation process, in which the twisting motion of thiophene rings is released, in this temperature region. Thus, it can be claimed that the twisting motion of P3HT thiophene rings is one of the determining factors of the photodynamics of P in P3HT films. This finding holds true for poly(thiophene)s with different alkyl lengths and should be considered in the design and construction of highly-functionalized organic devices based on poly(thiophene)s.

Phonons spreading from laser-heated gold nanoparticle array accelerate diffusion of excitons in an underlying polythiophene thin film

“…3c and e) show a slight delay of E200 fs in the position of the maximum of TA at 650 nm, which, respectively, suggests that the features at 650 and 1150 nm belong to different photochemical species. In agreement with Guo, et al 23 and Ogata, et al, 24 we adopted the interpretation of those species as polaron pairs (PP) and singlet excitons (S 1 ), respectively. Accordingly, we attribute the long-living feature at 950 nm, which becomes prevalent in NIR probe spectra on 10 ps timescale (see Fig.…”

“…This observation and interpretation agree well with previous reports of the time-resolved spectroscopic studies of P3HT thin films. [22][23][24] We further observed a positive TA feature generated immediately with laser excitation, at around 1150 nm (in Fig. 2d).…”

“…For the analysis of the kinetics in the NIR region we chose the spectral analysis approach inspired by the work of Ogata et al 24 It allowed us to project the spectrotemporal evolution into temporal evolution of weight parameters of the time invariant spectral features, without a priori knowledge of the model kinetic equation. The assumption of the time invariance of the spectral profiles is sound if the relevant processes contributing to the kinetics occur on a time-scale longer than vibrational relaxation processes associated with the reorganization energy of P3HT.…”

Fast P3HT Exciton Dissociation and Absorption Enhancement of Organic Solar Cells by PEG-Functionalized Graphene Quantum Dots

“…In pristine P3HT, the corollary photo‐induced absorption (PIA) effect is widely reported to begin at 620 nm and peak at 660 nm . If exciton dissociation is faster in GQD‐containing P3HT thin films, the absorption in this region is expected to be less than that of pristine P3HT.…”

Energy Transfer Kinetics in Photosynthesis as an Inspiration for Improving Organic Solar Cells

“…Possibly, the optical density for the polaron pair (PP) near 650 nm at the reference time is the maximum peak of ESA. 43 From this assumption, the conversion of the hot-exciton to PP should appear in a very short time scale (i.e., <0.5 ps). 43 Basco et al attributes this to an exciton dissociation mechanism in conjugated polymers, which can probably follow two pathways.…”