Fused Bithiophene Imide Dimer‐Based n‐Type Polymers for High‐Performance Organic Electrochemical Transistors

Abstract

The development of n-type organic electrochemical transistors (OECTs) lags far behind their p-type counterparts. In order to address this dilemma, we report here two new fused bithiophene imide dimer (f-BTI2)-based n-type polymers with abranched methyl end-capped glycol side chain, which exhibit good solubility,l ow-lying LUMO energy levels,f avorable polymer chain orientation, and efficient ion transport property, thus yielding aremarkable OECT electron mobility (m e )ofup to % 10 À2 cm 2 V À1 s À1 and volumetric capacitance (C*) as high as 443 Fcm À3 ,simultaneously.Asaresult, the f-BTI2TEG-FTbased OECTs deliver ar ecord-high maximum geometrynormalized transconductance of 4.60 Scm À1 and am aximum mC* product of 15.2 Fcm À1 V À1 s À1 .T he mC* figure of merit is more than one order of magnitude higher than that of the stateof-the-art n-type OECTs.T he emergence of f-BTI2TEG-FT brings an ew paradigm for developing high-performance ntype polymers for low-power OECT applications.

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

“…Overall, the amorphous and porous microstructures for p(C‐T) and p(N‐T) observed by AFM and GIWAX are expected to be the main driving force promoting 3D bulk doping needed for applications in OECT and thermoelectric devices. [ 29,48,49 ] On one hand, we postulate that electron charge transfer occurs in an interconnecting network of ordered islands surrounded by porous structure, yielding to the observed high mobility μ. On the other hand, the amorphous and disordered sites provide more free volume, accounting for the high ion transport for p(C‐T) and p(N‐T) .…”

“…Notably, all polymers have low‐lying LUMO, below −4.02 eV, a criterion needed to avoid electron trapping by water and oxygen. [ 22,29,43 ] We then estimated the HOMO level by subtracting the optical bandgaps ( E g,opt ) from the LUMO levels, leading to −5.53 eV for p(C‐T) , −5.76 eV for p(N‐T) , −5.43 eV for p(C‐2T) , and −4.98 eV for p(C‐g2T) , respectively.…”

“…Notably, all polymers have low-lying LUMO, below −4.02 eV, a criterion needed to avoid electron trapping by water and oxygen. [22,29,43] We then estimated the HOMO level by subtracting the optical bandgaps (E g,opt ) from the LUMO levels, leading to −5. Overall, the results show that the highly electron-deficient nature of the bis-azaisastin with respect to bis-isastin leads to the lowest-lying LUMO and HOMO levels of p(N-T) among these polymers.…”

“…[33,34] To date, most semiconducting polymers for OECTs are synthesized via transition-metal-mediated cross-coupling polymerizations, producing stoichiometric quantities of hazardous byproducts containing heavy metals, such as organostannane. [29,35] To address these critical issues, future materials design should integrate monomers enabling both high performance and synthesis via environmentally friendly and economic polymerization routes (e.g., aldol polycondensation). [33] Conjugated polymers comprising bisistain and lactone building blocks were introduced for organic field-effect transistors (OFET) and thermoelectrics.…”

“…To date, there are only four classes of n-type conjugated polymers for OECTs: naphthalene-1,4,5,8-tetracarboxylic-diimide-bithiophene (NDI)-based D-A conjugated polymers, [22][23][24][25][26][27] ladder-type poly(benzimidazobenzophenanthroline) (BBL) polymers, [22,28] fused electron-deficient lactam backbone PgNaN, [29] and, most recently, fused bithiophene imide dimer (f-BTI2)-based polymers, [30] and BBL152. [31] Among these, BBL152, through molecular weight engineering, exhibits the best reported performance, with a μC* of 25.9 F cm −1 V −1 s −1 and a g m,norm of 11.1 S cm −1 , slightly higher than f-BTI2 (μC* = 15.2 F cm −1 V −1 s −1 and g m,norm = 4.60 S cm −1 ), and one order of magnitude higher than PgNaN-based polymers (μC* = 0.78 F cm −1 V −1 s −1 and g m,norm = 0.21 S cm −1 ) and BBL (μC* = 0.60 F cm −1 V −1 s −1 and g m,norm = 0.3 S cm −1 ).…”