Influence of morphology of low-band-gap PCDTBT:PC71BM composite on photoinduced charge transfer: LEPR spectroscopy studyстатья
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Дата последнего поиска статьи во внешних источниках: 8 июня 2022 г.
Аннотация:The light-induced electron paramagnetic resonance (LEPR) study of spin charge carriers steady-state initiated by IR-Vis photons with the energy (wavelength) of 1.32 - 2.73 eV (940 - 455 nm) in organic composite of a low-band-gap poly(N-9'-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3′-benzothiadiazole)) (PCDTBT) with a [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) within a wide temperature region is reported. LEPR spectra of the PCDTBT:PC71BM composite were deconvoluted and the main resonance parameters of polarons and anion radicals of methanofullerene were determined. It has shown the reversible formation in polymer backbone of spin traps, whose number, distribution and depth governed by the photon energy. A part of photoinduced charge carriers is pinned by such traps resulting in formation in the composite of polymer and fullerene domains with different band gaps and photon sensitivity. Relaxation and dynamics parameters of all the charge carriers determined separately by the steady-state saturation method were shown to depend extremely on the energy of exciting photons. Polaron diffusion along polymer chains was analyzed in terms of spin interaction with the lattice phonons of crystalline domains embedded into an amorphous polymer matrix. Activation of polaron hopping over the energetic barrier is characteristic for the charge transfer between polymer chains. Small-angle librations of methanofullerene cages in a polymer matrix were shown to follow the Markus model. Our results suggest that C70-counter-ions embedded into the PCDTBT backbone deep an overlapping of molecular orbitals and provoke a layered morphology of appropriate composite. This orders polymer matrix, hinders the formation of spin traps and accelerates spin dynamics that facilitates charge transport through bulk heterojunctions. It was shown that the spin-assisted photon-electron conversion is realized in the composite within the visible and infrared regions of the sun spectrum with comparable effectiveness.