Molecular Weight Dependent Charge Carrier Mobility in Poly(3,3‘ ‘-dioctyl-2,2‘:5‘,2‘ ‘-terthiophene)

Abstract

Poly(3,3' '-dioctyl-2,2':5',2' '-terthiophene), a polymer recently used for the fabrication of organic field effect transistors, has been fractionated into five fractions distinctly differing in their molecular weights (Mn), with the goal of determining the influence of the degree of polymerization (DPn) on its principal physicochemical parameters. It has been demonstrated that within the Mn range studied (from 1.5 kDa to 10.5 kDa by SEC), corresponding to DPn from 10 to 38, the polymer band gap steadily decreases with growing molecular weight, which is clearly manifested by an increasing bathochromic shift of the band originating from the pi-pi* transition. The same trend is observed for the HOMO level, determined from the onset of the p-doping in cyclic voltammetry, which shifts from -5.10 eV to -4.90 eV for the lowest and the highest molecular weight fractions, respectively. The most pronounced influence of DPn has been found for the charge carriers' mobility-one of the most important parameters of field effect transistors (FETs) fabricated from this polymer. A fourfold increase in DPn results in an increase of the carriers' mobility by more than 3 orders of magnitude. Comparison of these results with those obtained for fractionated regioregular poly(3-hexylthiophene) shows a strikingly similar behavior of both polymers with respect to the molecular weight.

Computationally connecting organic photovoltaic performance to atomistic arrangements and bulk morphology

“…A discussion of the appropriate timescales and the justification of this assumption is given in the supplementary information (SI Section §2.1). This mobility calculation is more similar to time-of-flight experiments, where low excitation fluence, charge density, and active layer thickness are required [132,133], than field-effect transistor measurements on complete devices, which tend to report mobilities several orders of magnitude greater [134][135][136]. Figure 9.…”

Unexpectedly high field-effect mobility of a soluble, low molecular weight oligoquaterthiophene fraction with low polydispersity

“…For P3HT and other polythiophenes, the mobility was reported to increase systematically with molecular weight (MW) [2,6,8,10] (see e.g. Fig.…”

New Alternating Copolymers of 3,6‐Carbazoles and Dithienylbenzothiadiazoles: Synthesis, Characterization, and Application in Photovoltaics

“…[15c] These values can be related to the relatively low-molecular-weights of our polymers since the hole mobility of p-conjugated polymers is known to increase with the molecular weight over several orders of magnitude as was measured for different alkyl derivatives of polythiophene. [42][43][44] Indeed, PBTC, which has a higher polymerization degree compared to PCDTBT (respectively 8 compared to 3.6 based on SEC measurements), also has a higher hole mobility. Therefore in view of the application of these polymers to plastic solar cells, 3,6-linked polycarbazoles with higher molecular weights should be synthesized.…”