Concept of the time-dependent diffusion coefficient of polarons in organic semiconductors and its determination from time-resolved spectroscopy

0494710 - ÚMCH 2019 RIV US eng J - Článek v odborném periodiku
Rais, David - Menšík, Miroslav - Paruzel, Bartosz - Toman, Petr - Pfleger, Jiří
Concept of the time-dependent diffusion coefficient of polarons in organic semiconductors and its determination from time-resolved spectroscopy.
Journal of Physical Chemistry C. Roč. 122, č. 40 (2018), s. 22876-22883. ISSN 1932-7447. E-ISSN 1932-7455
Grant CEP: GA ČR(CZ) GA17-03984S; GA MŠMT(CZ) LTC17029
GRANT EU: European Commission(XE) MPNS COST Action MP1406
Institucionální podpora: RVO:61389013
Klíčová slova: diffusion coefficient * polaron * conducting polymers
Obor OECD: Polymer science
Impakt faktor: 4.309, rok: 2018

The population of photogenerated species in organic semiconductors may decay due to their mutual annihilation upon collisions during their diffusive motion. The standard kinetic models for the population decay, n(t), assume a time-invariant diffusion coefficient, i.e., D(t) ≡ constant. This leads to a failure in predicting the experimentally observed temporal evolution of photogenerated species if it asymptotically approaches a power-law decay n(t) ∼ t–x, with x < 0.5. We have used a concept of the time-dependent diffusion coefficient and developed a novel mathematical method of its determination from decay collision rates obtained by transient optical absorption spectroscopy. We tested the applicability of this method on the interpretation of data of the decay of polaron population obtained experimentally by time-resolved transient absorption measurements on thin films of regioregular poly(3-hexylthiophene), where we recently reported a power-law asymptote with x = 0.24. While we do not assume any microscopic origin of the time variance of D(t), we argue that, as the charge-carrier trapping states occupancy drops with decaying charge concentration, the carrier motion slows down. This argument is supported by a recent report on a molecular-scale model taking into account significant local anisotropy present in linear conjugated polymers. Our concept can be applied for the description of the evolution of species, like polarons or excitons, in various organic materials, provided their decay kinetics is controlled by a mutual annihilation during one- or three-dimensional diffusion.
Trvalý link: http://hdl.handle.net/11104/0288049