Influence of Molecular Weight on the Organic Electrochemical Transistor Performance of Ladder-Type Conjugated Polymers

Organic electrochemical transistors (OECT) hold promises for developing a variety of high-performance (bio-)electronic devices/circuits. While p-type polymers can routinely reach geometry-normalized transconductance (gm,norm) &gt; 100 S cm^-1 and volumetric capacitance (µC*) &gt; 300 F cm^-1 V^-1 s^-1 in OECTs, n-type polymers lag far behind in terms of performance with gm,norm &lt; 2 S cm^-1 and µC* values &lt; 7 F cm^-1 V^-1 s^-1. This performance mismatch between p-type and n-type OECTs hinders the development of power-efficient complementary devices/circuits. Here, we show that increasing the molecular weight of poly(benzimidazobenzophenanthroline) (BBL) from 4.9 to 51 kDa enables the development of n-type OECTs with record-high gm, norm (11.1 S cm^-1), µC* (25.9 F cm^-1 V^-1 s^-1), fast transient response down to 0.38 ms, and a threshold voltage of only 0.15 V. We used a combination of electrochemical analysis, UV-vis spectroelectrochemistry, dynamic light scattering, and X-ray diffraction data, to quantitatively characterize the impact of molecular weight on energetics, crystallinity, and charge transport properties of BBL. Finally, we demonstrated OECT-based complementary inverters with a record-high voltage gain of up to 100 V/V and ultra-low power consumption down to 0.32 nW. These inverters are among the best performing sub-1V complementary inverters reported to date. These findings demonstrate the importance of molecular weight to optimize the OECT performance of rigid organic mixed ionic-electronic conductors [1].<br/><br/><br/>[1] H. Y. Wu, C. Y. Yang, Q. Li, N. B. Kolhe, X. Strakosas, M. A. Stoeckel, Z. Wu, W. Jin, M. Savvakis, R. Kroon, D. Tu, H. Y. Woo, M. Berggren, S. A. Jenekhe, S. Fabiano, <i>Adv. Mater.</i> <b>2021</b>, <i>33</i>, 2106235, DOI: 10.1002/adma.202106235.