Blending Polymers for Improved Organic Thin Film Transistors

The deployment of smart packaging and wearable electronics depends on stable, low cost and high-performing electronics. Blending of polymers can provide a simple and low cost route towards obtaining optimized performance. This presentation will discuss our recent contributions towards 1) improving air stability and b) reducing operating voltage of n-type OTFTs using polymer blends.<br/><br/>1) N-type organic semiconductors are particularly susceptible to degradation by ambient air. we report the stabilization of n-type performance of the semiconductor poly{[N,N’-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5’-(2,29-bisthiophene)} (P(NDI2OD-T2)) when it is blended with an increasing proportion by weight of poly(2-vinylpyridine) (P2VP). The simple synthesis of P2VP also makes it an ideal candidate material for large-scale applications. Concentrations as low as 0.1% P2VP incorporated into the P(NDI2OD-T2) blends provided an immediate stabilization effect, and at 10% and 50%, longer-term stability after one week was observed.<br/><br/><i>Mater. Adv., 2023, 4, 4707-4711</i><br/><i>Adv. Electron. Mater.</i> 2024, 10, 2300660. https://doi.org/10.1002/aelm.202300660<br/><br/>2) Incorporating Poly methylmethacrylate (PMMA) as the dielectric successfully reduced the threshold voltage (VT) of bispentafluorophenoxy SiPc (F10-SiPc) based OTFTs from 14.9V to 7.3V while retaining a high mobility. Further reduction in VT was obtained by using copolymers and blends of PMMA and dimethylamino ethyl methacrylate (DMAEMA)-containing polymers where more mole fraction of DMAEMA led to a consistent drop in VT to 0.7 V. The electron donating groups of the tertiary amines in the DMAEMA show a clear interfacial doping of the semiconductor reducing the voltage required to populate the dielectric/semiconductor interface which charge carriers and turn on the device. Blending trace amounts of DMAEMA-containing copolymers with PMMA proved to be an effective strategy for reducing the VT while keeping the charge mobility high, unlike when using pure copolymers with elevated DMAEMA content. Time of flight secondary ion mass spectroscopy (ToF-SIMS) and X-ray photoelectron spectroscopy (XPS) demonstrated the DMAEMA containing copolymer is floating to the surface of the PMMA blend at the dielectric-semiconductor interface which explains the reduced VT. This study demonstrates a straightforward process for designing dielectric polymers and their blends for the reduction in VT for n-type OTFTs.<br/><br/><i>Adv. Electron. Mater.</i> 2024, 2300810. https://doi.org/10.1002/aelm.202300810<br/><br/>Overall, these studies demonstrate simple approaches to obtaining high performance OTFTs through simple functional polymer blending.