Green Synthesis of Lactone‐Based Conjugated Polymers for n‐Type Organic Electrochemical Transistors

Abstract

As new and better materials are implemented for organic electrochemical transistors (OECTs), it becomes increasingly important to adopt more economic and environmentally friendly synthesis pathways with respect to conventional transition-metal-catalyzed polymerizations. Herein, a series of novel n-type donoracceptor-conjugated polymers based on glycolated lactone and bis-isatin units are reported. All the polymers are synthesized via green and metal-free aldol polymerization. The strong electron-deficient lactone-building blocks provide low-lying lowest unoccupied molecular orbital (LUMO) and the rigid backbone needed for efficient electron mobility up to 0.07 cm 2 V −1 s −1 . Instead, polar atoms in the backbone and ethylene glycol side chains contribute to the ionic conductivity. The resulting OECTs exhibit a normalized maximum transconductance g m,norm of 0.8 S cm −1 and a μC* of 6.7 F cm −1 V −1 s −1 . Data on the microstructure show that such device performance originates from a unique porous morphology together with a highly disordered amorphous microstructure, leading to efficient ion-to-electron coupling. Overall, the design strategy provides an inexpensive and metal-free polymerization route for high-performing n-type OECTs.

Cyano‐Functionalized n‐Type Polymer with High Electron Mobility for High‐Performance Organic Electrochemical Transistors

“…The OECT devices of both polymers showed clear n-type accumulation-mode characteristics with almost negligible hysteresis in their transfer and output curves regardless of device gate voltage scan rate (Figures 3a-d, Table 2; with literature-reported channel materials for n-type OECTs; [38][39][40][41][42][43][44][45][46][47][48][49][50][51][52] please note the representative high-performance materials based on various electrondeficient building blocks are shown in color with displayed legends while the rest are shown in black.…”

“…This is also the first report of μ e,OECT > 0.1 cm 2 V −1 s −1 in n-type OECTs. [38][39][40][41][42][43][44][46][47][48]52] Meanwhile, the non-cyanated polymer f-BTI2g-TVT shows a much lower but still good μ e,OECT of 0.014 cm 2 V −1 s −1 , μC* of 1.50 F cm −1 V −1 s −1 , and g m,norm of 0.27 S cm −1 in n-type OECTs.…”

“…Since the pioneering work of p(gNDI-gT2) in 2016, [38] there are only limited number of reports on n-type materials for OECTs (please see summary in Table S1, Supporting Information). They mainly include donor-acceptor (D-A) polymers such as naphthalene diimde (NDI)-based P90, [39,40] p(C6-gNDI-gT2), [41] P(NDIMTEG-T), [42] P(C6-T2), [43] bithiophene diimide-based f-BTI2TEG-FT, [44] isoindigo-based AIG-BT, [45] lactone-based p(C-T), [46] and diketopyrrolopyrrolebased P(gPzDPP-CT2), [47] all-acceptor (A-A) ladder-type polymers BBL [48,49] and PgNaN, [50] small molecule C60-TEG. [51] n-Type organic mixed ionic-electronic conductors (OMIECs) with high electron mobility are scarce and highly challenging to develop.…”

“…Nonetheless, their OECT electron mobilities (μ e,OECT s) are much lower compared to the hole mobilities (μ h,OECT s, typically >0.1-1 cm 2 V −1 s −1 ), [25][26][27][28][29][30][31][32][33][34] ranging from 10 −5 to 10 −2 cm 2 V −1 s −1 with the highest value being 0.069 cm 2 V −1 s −1 in polymer p(C-T). [46] Therefore, it is highly challenging to simultaneously yield high electron mobility and ion transport capability to improve the μC* for n-type polymers. In order to improve μ e,OECT , various strategies have been employed such as side-chain engineering and backbone structure optimization, [41][42][43][44]46,47] increasing polymer molecular weight, [48] lowering device contact resistance.…”

“…[46] Therefore, it is highly challenging to simultaneously yield high electron mobility and ion transport capability to improve the μC* for n-type polymers. In order to improve μ e,OECT , various strategies have been employed such as side-chain engineering and backbone structure optimization, [41][42][43][44]46,47] increasing polymer molecular weight, [48] lowering device contact resistance. [58] To this end, utilizing the rich library of electrondeficient building blocks, which have been successful in building a great number of high mobility n-type polymers for organic thin-film transistors (OTFTs), [59][60][61][62] is considered as an effective approach to construct n-type OECT materials.…”