Electron and Hole Dynamics on Isolated Chains of a Solution‐Processable Poly(thienylenevinylene) Derivative in Dilute Solution

Abstract

Poly(thienylenevinylene)s (PTVs) are p-conjugated polymers with great potential for use in electronic devices. In thin films, they have been shown to be good p-type conductors (positive charge mobility ca. 10 ±3 cm 2 V ±1 s ±1 ) but no n-type conduction has been reported. In order to investigate the mobility and dynamics of the charge carriers on PTVs at the molecular level, we used pulses of ionizing radiation to generate charges on PTV molecules in dilute solution, i.e., isolated from intermolecular interactions between polymer chains. The mobility of the charge carriers and the kinetics of their decay were monitored by time-resolved microwave conductivity (TRMC) measurements at a frequency of 34 GHz. It was found that both electrons and holes have a high mobility along the isolated polymer chains (0.23 ± 0.04 and 0.38 ± 0.02 cm 2 V ±1 s ±1 , respectively). The electrons were observed to become trapped at defects or impurities within 4 ls. No trapping was observed COMMUNICATIONS 718

Effect of intermolecular disorder on the intrachain charge transport in ladder-type poly(p-phenylenes)

“…Since this effective mass is comparable to the effective mass for charges in inorganic semiconductors, the mobility of charge carriers along a perfectly ordered polymer chain is expected to be in the same order of magnitude as the mobility found for inorganic semiconductors, i.e., in the order of 1000 cm 2 /V s. 11 Indeed a value of 600 cm 2 /V s has been found for the mobility of holes along isolated ladder-type poly͑paraphenylene͒ chains in dilute solution by time-resolved microwave conductivity ͑TRMC͒ measurements. 12 However, the values found for the device mobility in conjugated polymers, range from 10 −7 -10 −2 cm 2 / V s, for derivatives of poly͑para-phenylenvinylene͒, poly͑thienylene-vinylene͒, poly͑thiophene͒, and ladder-type poly͑para-phenylene͒. 4,[13][14][15] These values are several orders of magnitude lower than expected on the basis of the arguments above.…”

“…Therefore, the intrachain mobility of charges along isolated polymer chains is monitored in TRMC measurements on dilute solutions. 12,17,33,34 Since the chain-length dependence for the real mobility observed for the ladder-type polymer in solid samples is the same as the chain-length dependence observed for isolated ladder-type polymer chains, we conclude that the intrachain motion of charges is monitored in the experiments on solid samples described here.…”

“…Taking into account the random orientation of the polymer chains and the linear polarization of the microwave field, these two quantities are related by 1D =3 iso . 12 The real and imaginary parts of the lower limit to the sum of the intrachain hole and electron mobility are denoted by ⌺ min,re 1D and ⌺ min,im 1D , respectively.…”

“…Contact effects are the most important of the device-specific properties and determine the performance of organic optoelectronic devices to a large extent. 12,16 Two examples of intrinsic properties of organic materials that limit the charge carrier mobility are interchain transport and charge transport over grain boundaries ͑bound-ary junctions between different relatively ordered domains within the sample͒. Both processes are expected to be significantly slower than intrachain transport and depend strongly on the material morphology on a supramolecular scale.…”

Charge transport along phenylenevinylene molecular wires

“…PR-TRMC measurements have been performed for a variety of conjugated polymers and it has been found that the mobility of charges along isolated conjugated polymer chains depends strongly on the structure of the backbone. [16][17][18][19] In order to interpret and exploit the experimental data available from the measurements mentioned above it is essential to have a detailed theoretical framework describing charge transport along molecular wires. [20] The elementary processes in charge transport along conjugated polymers are similar to two-centre charge transfer reactions [21] where the efficiency of transfer depends on the energy difference and the electronic coupling (charge transfer integral) between the sites involved.…”