Self-assembly of poly (ionic liquid) block copolymer based dielectrics on semiconductor formation and performance

Abstract

Wearable, disposable, implantable and lightweight electronic devices all require low power consumption, typically less than 3 V. Polymerized ionic liquids represent an emerging class of dielectric materials which can enable low voltage organic thin film transistor operation (OTFT) while in the solid state, reducing the potential for toxic or flammable electrolyte leaks. Here we show that bottom gate bottom contact OTFTs were successfully fabricated using a library of 12 poly-(styrene)-b-poly(1-(4-vinylbenzyl)-3-butylimidazolium-r-poly(ethylene glycol) methyl ether methacrylate) block copolymers with varying VBBI⁺ and PEGMA ratios, and can achieve OTFTs that turn on between 0 and 1 V. We demonstrate that the poly(ionic liquid) microstructure dictates the self-assembly which correlates to OTFT performance. Notably, we indicate that changing the surface chemistry of the substrate the poly(ionic liquid) is cast on is less significant in driving block copolymer self-assembly compared to block ratios and the counter ion. We also report that the semiconductor crystalline domains are similar when deposited on the poly(ionic liquids), however the films differ in terms of semiconductor molecular order in the amorphous domains. Overall, we demonstrate that device performance is primarily linked to the poly(ionic liquid) self-assembly, while also highlighting the importance of both the crystalline and amorphous domains in the semiconductor structure of thin films.