Molecular Weight Dependence of Exciton Diffusion in Poly(3‐hexylthiophene)

Abstract

We present a joint experimental and theoretical study of singlet exciton diffusion in spincoated P3HT films and its dependence on molecular weight. The results show that exciton diffusion is fast along the co-facial π-π aggregates of polymer chromophores and about 100 times slower in the lateral direction between aggregates. Exciton hopping between aggregates is found to show a subtle dependence on interchain coupling, aggregate size and Boltzmann statistics. Also a clear correlation is observed between the effective exciton diffusion coefficient, the degree of aggregation of chromophores and exciton delocalisation along the polymer chain, which suggests that exciton diffusion length can be enhanced by tailored synthesis and processing conditions. Submitted to 2

Tuning crystalline ordering by annealing and additives to study its effect on exciton diffusion in a polyalkylthiophene copolymer

“…As a result, one exciton is lost per encounter. 31,32 Fluorescence decays measured at different excitation densities are shown in ESI † (Fig. S3).…”

“…We used a sum of three exponential functions to describe this decay and to obtain the empirical time-dependent k(t). The rate constant for diffusion-limited annihilation in a three-dimensional isotropic system can be described by a sum of a time-independent term and of a time-dependent term 32,33 gðtÞ…”

“…Eqn (2) assumes that only one exciton is lost per encounter. The value of R a was experimentally determined in P3HT to be 1.8 nm 31,32 and we use this value for the copolymer studied here because it shows similar packing to P3HT as observed by Grazing Incidence X-ray scattering (GIXS). 30 The magnitude of R a depends on the spectral overlap of fluorescence with excited state absorption which is unlikely to change significantly with different processing because changes in ground state absorption and fluorescence spectra are small (vide infra).…”

Carrier Transport Enhancement in Conjugated Polymers through Interfacial Self-Assembly of Solution-State Aggregates

“…This observation further supports a growing body of work suggesting that local order may be more crucial to improving the operation of polymer-based OTFTs. 13,17,66,[69][70][71][72] As mentioned above, the structural and optical analyses are bulk measurements, whereas transport measurements in the context of OTFTs is far more sensitive to the polymer order and conformation at the interface. 11 Since surface functionalization has an enhancing effect limited to within approximately 10 nm of the modified interface, 11,40 we speculate that the measured improvements in local order averaged over the entire film depth may be even more pronounced at the interface, perhaps explaining the dramatic enhancement of carrier mobility by nearly two orders of magnitude.…”

Organic solar cells based on acceptor-functionalized diketopyrrolopyrrole derivatives

“…Smaller aggregates are desirable allowing increased interfacial area and better charge separation. 26 This, in general, results in an increase in J sc and hence an enhanced overall device performance. 27 The domain sizes in the present study are much larger than the optimal required for efficient exciton dissociation.…”