Abstract
Organic field-effect transistors (OFETs) represent a low-cost transistor technology for creating next-generation large-area, flexible and ultra-low-cost electronics. Conjugated electron donor-acceptor (D-A) polymers have surfaced as ideal channel semiconductor candidates for OFETs. However, high-molecular weight (MW) D-A polymer semiconductors, which offer high field-effect mobility, generally suffer from processing complications due to limited solubility. Conversely, the readily soluble, low-MW D-A polymers give low mobility. We report herein a facile solution process which transformed a lower-MW, low-mobility diketopyrrolopyrrole-dithienylthieno[3,2-b]thiophene (I) into a high crystalline order and high-mobility semiconductor for OFETs applications. The process involved solution fabrication of a channel semiconductor film from a lower-MW (I) and polystyrene blends. With the help of cooperative shifting motion of polystyrene chain segments, (I) readily self-assembled and crystallized out in the polystyrene matrix as an interpenetrating, nanowire semiconductor network, providing significantly enhanced mobility (over 8 cm2V−1s−1), on/off ratio (107), and other desirable field-effect properties that meet impactful OFET application requirements.
Highlights
There remain several critical materials and process challenges yet to be resolved for practical applications
We report our studies on medium-assisted self-assembly of a solution processable, lower-molecular weights (MW), low-mobility diketopyrrolopyrrole-dithienylthieno[3,2-b]thiophene (DPP-DTT) polymer semiconductor, (I) as shown in Fig. 1, into high crystalline orders in a semiconductor film system for enhanced charge transport efficacy
Unlike earlier reported vertical phase separation of semiconductor/polymer blends which separated into two layers[25,28,29,30,31,33], (I) in the polystyrene blend underwent segregation and self-assembly into higher crystalline orders and crystallized out within the polystyrene matrix
Summary
There remain several critical materials and process challenges yet to be resolved for practical applications. A wide variability in OFET performance results when a high-MW polymer semiconductor is utilized Another practical difficulty is the synthetic challenge in obtaining high-MW polymer semiconductors due to premature precipitation of lower-MW polymer intermediates out of reaction media during synthesis. It would be highly desirable and of great practical significance if a soluble, low-MW polymer semiconductor can be processed into a channel semiconductor of higher crystalline orders to improve its mobility. These are primarily solvency-controlled crystallization from “marginal” solvents or phase separation of semiconductor molecules into higher crystallinity in inert polymer blends[20,29,32] Many of these reported processing procedures to enhance charge transport properties of organic semiconductors are neither amenable to common printing techniques nor readily scalable for practical adoption. These OFET properties are functionally more than sufficient for many impactful electronic applications (e.g., display backplane electronics, ultra-low-cost radio-frequency identification tags, etc.)[17]
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