Revealing the Role of Polaron Distribution on the Performance of n-Type Organic Electrochemical Transistors

Abstract

Organic electrochemical transistors (OECTs) have shown great potential in bioelectronics and neuromorphic computing. However, the low performance of n-type OECTs impedes the construction of complementary-type circuits for low-power-consumption logic circuits and high-performance sensing. Compared with their p-type counterparts, the low electron mobility of n-type OECT materials is the primary challenge, leading to low μC* and slow response speed. Nevertheless, no successful method has been reported to address the issue. Here, we find that the charge carrier mobility of n-type OECTs can be significantly enhanced by redistributing the polarons on the polymer backbone. As a result, 1 order of magnitude higher electron mobility is achieved in a new polymer, P­(gPzDPP-CT2), with a simultaneously enhanced μC* value and faster response speed. This work reveals the important role of polaron distribution in enhancing the performance of 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.…”

“…Both f-BTI2g-TVT and f-BTI2g-TVTCN show good solubility in chloroform, and their chemical structure and purity were verified by NMR and elemental analysis. From gel permeation chromatography (GPC) using hexafluoroisopropanol as eluent (Figures S1 and S2, Supporting Information), [30,47] their molecular weight (M n )/polydispersity index (Đ) were found to be 42.9 kDa/3.4 and 28.3 kDa/4.8 for f-BTI2g-TVT and f-BTI2g-TVTCN (Table 1), respectively. Differential scanning calorimetry scans (Figure S3a, Supporting Information) showed no distinctive thermal transitions for both polymers in the temperature range of 50-250 °C, further thermogravimetric analysis (Figure S3b, Supporting Information) indicated their high thermal stability with decomposition temperatures of >320 °C (defined by 5% weight loss) which are adequate for OECT device application.…”

“…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.…”

“…[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.…”