Influence of molecular weight on the short‐channel effect in polymer‐based field‐effect transistors

Abstract

In this study, we demonstrate how the intrinsic properties of a polymer can influence the electrical characteristics of organic field-effect transistors (OFETs). OFETs fabricated with three batches of poly[2-methoxy,5-(3 0 ,7 0 -dimethyl-octyloxy)]p-phenylene vinylene (MDMO-PPV) were investigated. The properties of the polymers were initially investigated using Fourier transform infrared spectroscopy (FTIR), impedance spectroscopy (IS), gel permeation chromotography (GPC), and cyclic voltammetry (CV), respectively. The structure and purity of the polymer batches were found to be very comparable, but the molecular weight (M n and M w ) and polydispersity (PDI ¼ M w /M n ), varied between the samples and the HOMO and LUMO levels of the polymers were found to depend on the molecular weight properties. OFETs were then fabricated with the polymers and electrically characterized. It was observed that the channel current and the field-effect mobility increase with increasing polymer molecular weight. The output characteristics of the transistors, on the other hand, were found to depend on the PDI of the polymer. Saturation of the channel current occurs at higher source-drain voltages and short-channel behavior was observed to start at longer channel lengths for polymers with a higher PDI. This behavior is observed to be thickness dependent, and the shortchannel behavior was more pronounced for thicker MDMO-PPV films. These results are explained in terms of influences of chain packing and ordering and high bulk currents on the FET output and transistor parameters.

Energetics of Solvent-Based Deposition of Fullerene Derivative on the Inorganic–Organic Hybrid Lead Halide Perovskite Surface

“…Solution processable thin-film organic electronic devices, − such as planar perovskite solar cells (PSCs), − organic photovoltaic solar cells (OPVs), organic light emitting diodes (OLEDs), , and organic field-effect transistors (OFETs), − hold excellent promise as lightweight, flexible, and cost-effective devices. Low temperature solution processing of thin films of active materials, employing spin coating and spray coating, is a cost-effective and high-throughput technique for fabrication of electronic devices. , However, the reliability and reproducibility of solution-processed thin films as well as controlling the resulting morphology poses a significant challenge .…”

Influence of Simultaneous Tuning of Molecular Weights and Alkyl Substituents of Poly(thienoisoindigo-alt-naphthalene)s on Morphology and Change Transport Properties

“…On the other hand, some recent studies have begun to observe that the molecular weight and the alkyl substituent of a given polymer platform have a profound influence on molecular ordering and microstructure, and additionally on optoelectronic and charge transport characteristics, thus making it one of the key parameters governing the device performance. ,− For example, it was found that not only increasing the molecular weight but also decreasing the distance of the branching point of branched alkyl chains to backbones and their bulkiness and are linked to improved charge transport arising from better intergrain connectivity. , However, in most cases, the effects of molecular weight and alkyl substituent variations on polymer properties and device performances have been studied independently. ,,− To the best of our knowledge, there are only a few reports on a structure–property relationship regarding the simultaneous tuning of molecular weight and alkyl substituents, , which has to be further investigated.…”

Recent Advances in Polymer Organic Light-Emitting Diodes (PLED) Using Non-conjugated Polymers as the Emitting Layer and Contrasting Them with Conjugated Counterparts

“…For example, the effects of molecular weight and polydispersity of the polymers on the PLED performance are still underexplored. Although a few previous studies were conducted, 33,34,126,127 much more work has to be done to gain conclusions of enhanced generalities and also to obtain more solid understanding on the structure-property relationships in PLED materials. In addition, the purity of polymers for PLED applications should always be verified to establish a reliable link between device performances with the structure of the polymer employed in the device.…”

“…Polydispersity index (PDI) has a significant impact on the effective conjugation length homogeneity of the polymer chains which in turn affects the emission colors, formation of undesirable charge traps and interchain packing in the polymer. 33,126,127 Fig. 27.…”