Enhanced Environmental Stability Induced by Effective Polarization of a Polar Dielectric Layer in a Trilayer Dielectric System of Organic Field-Effect Transistors: A Quantitative Study

Abstract

We report a concept fabrication method that helps to improve the performance and stability of copper phthalocyanine (CuPc) based organic field-effect transistors (OFETs) in ambient. The devices were fabricated using a trilayer dielectric system that contains a bilayer polymer dielectrics consisting of a hydrophobic thin layer of poly(methyl methacrylate) (PMMA) on poly(vinyl alcohol) (PVA) or poly(4-vinylphenol) (PVP) or polystyrene (PS) with Al2O3 as a third layer. We have explored the peculiarities in the device performance (i.e., superior performance under ambient humidity), which are caused due to the polarization of dipoles residing in the polar dielectric material. The anomalous behavior of the bias-stress measured under vacuum has been explained successfully by a stretched exponential function modified by adding a time dependent dipole polarization term. The OFET with a dielectric layer of PVA or PVP containing hydroxyl groups has shown enhanced characteristics and remains highly stable without any degradation even after 300 days in ambient with three times enhancement in carrier mobility (0.015 cm(2)·V(-1)·s(-1)) compared to vacuum. This has been attributed to the enhanced polarization of hydroxyl groups in the presence of absorbed water molecules at the CuPc/PMMA interface. In addition, a model has been proposed based on the polarization of hydroxyl groups to explain the enhanced stability in these devices. We believe that this general method using a trilayer dielectric system can be extended to fabricate other OFETs with materials that are known to show high performances under vacuum but degrade under ambient conditions.

Highly Efficient Flexible Organic Light Emitting Transistor Based on High‐k Polymer Gate Dielectric

“…As shown in Figure d, the device exhibits a saturated mobility of 1.38 cm 2 V −1 s −1 at a very low threshold voltage of −1.9 V. Besides, it also shows a small hysteresis with a high on/off ratio of 1.2 × 10 5 . The increasing carrier mobility could be attributed to the enhanced polarization of hydroxyl groups in the presence of water molecules at the C8‐BTBT/CYTOP interface . The device shows a maximum brightness of 13 400 cd m −2 at V g = −24 V and V d = −24 V (Figure b), which is higher than device B1.…”

Polyimide/polyvinyl alcohol bilayer gate insulator for low-voltage organic thin-film transistors

“…Inorganic/organic bilayer and inorganic multilayer structures could suppress the through-plane leakage current by termination of the defects, grain boundaries, and clusters in the films [14,30,31]. It was reported that polymer/polymer bilayer structures could reduce the leakage current by tuning the surface morphology and termination of the pinholes [32][33][34]. Fig.…”

Tailoring the Dielectric Layer Structure for Enhanced Performance of Organic Field-Effect Transistors: The Use of a Sandwiched Polar Dielectric Layer

“…Since PVA and PVP are polar polymers with abundant hydroxyl groups attached to polymer chains, the polarizations of hydroxyl dipoles would be sensitive to the magnitude and direction of the electrical field (bias) [27]. The influence of applied gate bias on the orientation of hydroxyl groups in the PVA layer was studied by Tsai et al [20].…”

“…The performance and stability of OFETs were improved [27], but the third layer Al 2 O 3 was grown by converting a portion of Al film by an anodization process, even the annealing temperature of the solution process Al 2 O 3 was at least 150 °C [28], which was not compatible with plastic substrates [29]. In this work, we demonstrate a trilayer dielectric system consisting of a polar dielectric layer inserted between hydrophobic polymer layers, which is fabricated with a solution process.…”