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The charge carrier mobility along a molecular wire of fluorene-thiophene copolymers represented by poly-(9,9 0 -di-n-octylfluorene-co-bithiophene): F8T2 is investigated by flash-photolysis time-resolved microwave conductivity. We systematically examined the impacts of the number of oligothiophene units, their composition ratios, and molecular weights. It is revealed that the oddÀeven number of oligothiophene units has a significant effect on the mobility if they are incorporated into the polyfluorene backbone in high ratio. The structural dependence study and the observed high intramolecular mobility of about 1 cm 2 V À1 s À1 could be helpful for the design of novel multicomponent conjugated copolymers and its application in organic electronic devices.

The impacts of solvent and thermal annealing on the mobility and photogeneration efficiency of free charge carriers in regioregular poly(3-hexylthiophene) were investigated by flashphotolysis time-resolved microwave conductivity measurements, transient absorption spectroscopy of the perylenediimide radical anion, and photocurrent measurements of a comb-type interdigitated electrode. A respectable high mobility of 0.62 cm 2 V ¹1 s ¹1was found as a three-dimensional value, highlighting the unprecedented electronic nature of the conjugated polymer.Regioregular polythiophene 1 is a diverse platform of conjugated polymers, and a growing number of studies have also made use of organic field-effect transistors (FETs) 2 and organic photovoltaics (OPV). 3 The highest FET hole mobility in poly(3-hexylthiophene) (P3HT) reported so far is 0.10The side-chain engineering of polythiophene 4 yielded analogues such as poly(3,3¤¤¤-dialkyl-quarter-thiophene) (PQT) 5 Despite the advent of new families of polythiophene derivatives, P3HT has occupied an important place, in particular, in bulk heterojunction OPV devices, because it shows a high power conversion efficiency (PCE) of 45% in combination with [6,6]-phenyl C 61 butyric acid methyl ester (PCBM) 3b,3c and 67% with the indeneC 60 bisadduct (ICBA). 9 The high external quantum efficiency in the visible region, attributed to the high hole mobility and charge-separation efficiency, allowed the realization of a tandem cell with the top-ranked performance using P3HT/ICBA blends as the front cell. 10High charge-carrier mobilities of conjugated polymers have been demonstrated by using a direct current method represented by FET device characterization, 11 with observation of a pronounced dependence of the mobility not only on the choice of materials but also on the device structures, 12 surface modification, 13 and processing conditions.2 In this letter, we report our investigation on the local charge-carrier mobility of organic semiconductors through flash-photolysis time-resolved microwave conductivity (FP-TRMC) measurements.14 For the fully experimental determination of mobility, we utilized transient absorption spectroscopy (TAS) of the perylenediimide radical anion, which is a viable approach for estimation of the photogeneration efficiencies of free charge carriers (º).14f Furthermore, we examined the photocurrent of polymer-coated comb-type interdigitated metal electrodes to establish whether this direct-current method is applicable for the determination of º. P3HT and N,N¤-bis(2,5-di-tert-butylphenyl)-3,4,9,10-perylenedicarboximide (PDI, Figure 1a) blend films were prepared with the desired weight ratio by drop-casting of chlorobenzene (CB), chloroform (CF), or o-dichlorobenzene (DCB) solution onto a cleaned quartz plate and drying in a vacuum oven at room temperature. Figure 1b shows the photoconductivity transients of P3HT/PDI blend films, where the vertical axis º® represents the product of the photogeneration efficiency of the free charge carriers, º, and the sum of t...

We investigated the effect of the triphenylamine (TPA) content of TPA–fluorene copolymers on their charge carrier mobilities. Intramolecular mobilities were measured by flash-photolysis time-resolved microwave conductivity (TRMC), while intermolecular hole mobilities were determined on the basis of space-charge limited current (SCLC) and field-effect transistor (FET). TRMC and SCLC except for FET showed an analogous dependence on the TPA content. The results are discussed from the viewpoints of delocalization of singly-occupied molecular orbital of radical cation, conformation of polymer chain, and trap effect. This study highlights the importance of optimizing the TPA content in the polyfluorene backbone for electronic device application.

Optoelectronic and optical properties of poly(3-alkylthiophene) (P3HT) diluted in polystyrene (PS) matrices were investigated by flash-photolysis time-resolved microwave conductivity (FP-TRMC) and steady-state photoabsorption spectroscopy, respectively. We examined intra-and inter-molecular charge carrier mobilities in the blend and pristine P3HT films and found the contribution of inter-molecular one is half at the maximum in the pristine film. This in turn gave information about the minimum one-dimensional intra-molecular mobility of 0.18 cm 2 /Vs.