The effect of air exposure on device performance of flexible C8-BTBT organic thin-film transistors with hygroscopic insu
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Published online 13 October 2020 | https://doi.org/10.1007/s40843-020-1489-6
The effect of air exposure on device performance of flexible C8-BTBT organic thin-film transistors with hygroscopic insulators *
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Pengshan Xie, Tianjiao Liu, Pei He, Guozhang Dai, Jie Jiang, Jia Sun and Junliang Yang ABSTRACT Organic thin film transistors (OTFTs) are normally sensitive to ambient conditions and show performance degradation in air. On the contrary, the performance of flexible 2,7-dioctyl[1] benzothieno [3,2-b][1]benzothiophene (C8-BTBT) OTFTs using cross-linked polymer layer, poly(4vinyl-phenol)-4,4'-(hexafluoroisopropylidene) diphthalic anhydride (PVP-HDA), as the dielectric layer can be improved in air conditions with 40% relative humidity. Under soaking in air with 40% relative humidity, the electrical behavior, surface morphology, and contact angle of the flexible C8-BTBT OTFTs using PVP-HAD as dielectric layer with three different thicknesses were investigated. It is found that, when the devices with 375 nm-thick PVP-HDA films are placed in 40% relative humidity air conditions for 6 h, the corrected average 2 −1 −1 mobility (µ) can increase from 3.2 to 5.1 cm V s . Furthermore, the average threshold voltage (Vth) changes from 4 −12.4 to −9.3 V while keeping a constant ratio of Ion/Ioff = 10 . These results indicate that the flexible C8-BTBT OTFTs with PVP-HDA dielectric layer exhibit interesting application prospects. Keywords: flexible electronics, C8-BTBT, OTFTs, PVP-HDA, hygroscopicity, air stability.
INTRODUCTION Over the past years, significant developments in organic thin film transistors (OTFTs) have been made, and the 2 −1 −1 mobility (µ) has been increased to over 43 cm V s [1]. It is well known that OTFTs have the advantages of solution process, flexibility, low cost, large area, and so on [2–5]. Thus, OTFTs show great potential applications in sensors, circuits, and synaptic electronics [6–11], also thanks to the improvement of device performance via new active materials, device engineering, interface en-
gineering of dielectric layer, etc. [12–16]. Air stability is one of the most important issues for meeting the requirements in practical applications [17–21]. In previous studies, organic materials affected by air environment have been widely studied [22,23]. It has been reported that for gate dielectric materials with active functional groups, such as hydroxyl groups, the interaction with the adsorbed water in air would affect the device performance [24,25], leading to performance degradation in air [26,27]. As a typical gate dielectric layer material, cross-linked polymer, poly(4-vinyl-phenol)-4,4'-(hexafluoroisopropylidene) diphthalic anhydride (PVP-HDA), can be prepared via solution processes and exhibits excellent insulating properties [28]. Furthermore, 2,7-dioctyl[1] benzothieno[3,2-b][1]-benzothiophene (C8-BTBT) is one of the most promising high-mobility p-channel semiconductor material in OTFTs [29–31]. Herein, the effect of air exposure with 40% relative humidity on the device performance of
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