Synergistic Effect of Multi‐Walled Carbon Nanotubes and Ladder‐Type Conjugated Polymers on the Performance of N‐Type Organic Electrochemical Transistors

Silan Zhang,Magnus Berggren,Tero‐Petri Ruoko,Renee Kroon,Chi‐Yuan Yang,Ziang Wu,Deyu Tu,Mats Fahlman,Yoonjoo Lee,Christian Müller,Xianjie Liu,Simone Fabiano,Han Young Woo,Per O Å Persson,Matteo Massetti

doi:10.1002/adfm.202106447

Abstract

AbstractOrganic electrochemical transistors (OECTs) have the potential to revolutionize the field of organic bioelectronics. To date, most of the reported OECTs include p‐type (semi‐)conducting polymers as the channel material, while n‐type OECTs are yet at an early stage of development, with the best performing electron‐transporting materials still suffering from low transconductance, low electron mobility, and slow response time. Here, the high electrical conductivity of multi‐walled carbon nanotubes (MWCNTs) and the large volumetric capacitance of the ladder‐type π‐conjugated redox polymer poly(benzimidazobenzophenanthroline) (BBL) are leveraged to develop n‐type OECTs with record‐high performance. It is demonstrated that the use of MWCNTs enhances the electron mobility by more than one order of magnitude, yielding fast transistor transient response (down to 15 ms) and high μC* (electron mobility × volumetric capacitance) of about 1 F cm−1 V−1 s−1. This enables the development of complementary inverters with a voltage gain of >16 and a large worst‐case noise margin at a supply voltage of <0.6 V, while consuming less than 1 µW of power.

Highlights

The acid treatment results in well-dispersed multi-walled carbon nanotubes (MWCNTs) with an average diameter of about 13 nm and length of about ≈1–2 μm (Figure 2e and Figure S1, Supporting Information), and with a surface functionalized with carboxylic acid groups as shown by infrared spectroscopy measurements
BBL was dissolved in methanesulfonic acid (MSA), whereas the acid-treated MWCNTs were dispersed in isopropanol (IPA)
Note that we estimated the charge carrier mobility through the constant gate current[7c] and impedance matching[25] methods and observed similar trends (Figure S18, Supporting Information). These mobility values are 1–3 orders of magnitude higher than those reported for NDI-based polymers used in Organic electrochemical transistors (OECTs) (Table S1, Supporting Information), and on par with thiophene-based polymers used in accumulation-mode transistors (≈1.3 × 10−3 cm2 V−1 s−1).[5c,13,15,26] In the case of BBL+MWCNT mix-ink, the electron mobility is observed to be almost independent of the MWCNT content

Summary

Results and Discussion

The BBL/MWCNT peak area ratio decreases with increasing the content of MWCNTs for both co-ink and mix-ink films (Figure S7d, Supporting Information). Note that we estimated the charge carrier mobility through the constant gate current[7c] and impedance matching[25] methods and observed similar trends (Figure S18, Supporting Information) These mobility values are 1–3 orders of magnitude higher than those reported for NDI-based polymers used in OECTs (Table S1, Supporting Information), and on par with thiophene-based polymers used in accumulation-mode transistors (≈1.3 × 10−3 cm V−1 s−1).[5c,13,15,26] In the case of BBL+MWCNT mix-ink, the electron mobility is observed to be almost independent of the MWCNT content (average mobility ≈0.5 × 10−3 cm V−1 s−1). Since NM is proportional to −1/ (gain), BBL:MWCNT 10:1 based inverters show the highest gain as well as the highest NML and NMH

Conclusions

Experimental Section

Data Availability Statement