Aerosol Jet Printed Organic Electrochemical Transistors using n-Type Naphthalene Dimide-Based Small-Molecule Organic Mixed Ionic-Electronic Conductor

Organic semiconductors are capable of transporting both the ionic and electronic charges representing a new class of material: organic mixed ionic-electronic conductor (OMIECs). OMIECs have been used for a variety of organic electronics, including organic electrochemical transistors (OECTs) and energy conversion/storage devices. Most reported OMIECs are hole-transporting p-type polymeric material, such as PEDOT:PSS and polythiophene derivatives. In contrast, electron-transporting n-type OMIECs are less reported and often have poorer performance and stability, despite their need in fabricating complementary circuits or biosensors that require electron transfer. Compared to polymeric OMIECs, small-molecule mixed conductors offer significant potential thanks to their mono-dispersity and synthesis simplicity.¹⁾<br/>We recently reported the first naphthalene-diimide-based n-type small-molecule organic mixed ionic-electronic conductors and their utilization as a channel material in accumulation mode organic electrochemical transistors. The glycolated naphthalene diimide n-type OMIEC, gNDI-Br₂, was characterized for its electrochemical behaviour and used to fabricate an OECT via a simple drop-casting technique. The gNDI-Br₂ OECT operated as an n-type accumulation mode and showed a maximum transconductance (g_m, _max) of 814 ± 124.2 μS and a mobility capacitance product (μC^*) of 0.23 ± 0.04 F cm^-1V^-1s^-1.²⁾<br/>The transconductance of the OECT is affected by its intrinsic material figure-of-merit (μC^*) and channel geometry.³⁾ Drop-casted gNDI-Br₂ devices pose a challenge for practical applications due to their unpredictable channel geometry and hence their repeatability. To resolve this issue, we fabricated gNDI-Br₂ OECTs using an aerosol-jet 3D printing technique with the Optomec Aerosol Jet 5X 3D printer. This method creates the sub-micron size aerosols using ultrasonic atomization which are deposited onto the substrate via a nozzle.⁴⁾ Owing to the AJ5X 3D printing system, we were able to manipulate the OECT channel geometry and fabricate repeatable OECT devices.<br/>Additionally, for the aerosol jet printing, the gNDI-Br₂ solution with low evaporation rate was required while transitioning to an aerosol. By using low-volatile solvent for the solution and aerosol-jet 3D printing, the gNDI-Br₂ molecules were evenly distributed onto the substrate, resulting in higher crystallinity as compared to the drop-casted OECTs. This resulted in an improved performance of the gNDI-Br₂ OECT (g_m, _max = 1.12 mS, μC^* = 0.75 F cm^-1V^-1s^-1). Moreover, we achieved a fully printed n-type OECT by printing other component, including metal electrodes onto flexible polymer substrates. Using this gNDI-Br₂ OECT, we were able to fabricate aerosol-jet printed complementary logic circuit with a PEDOT:PSS p-type counterpart.<br/><br/>Reference<br/>1) S. Yu, C.J. Kousseff, C.B. Nielsen, n-Type semiconductors for organic electrochemical transistor applications, <i>Synth. Met</i>. 293 (2023) 117295.<br/>2) S. Kang, J. Fan, M. Gupta, Naphthalene diimide-based n-type small molecule organic mixed conductors for accumulation mode organic electrochemical transistors, <i>RSC Adv</i>. 13 (2023) 5096-5106.<br/>3) D.A. Bernards, G.G. Malliaras, Steady-state and transient behavior of organic electrochemical transistors. <i>Adv. Funct. Mater</i>. 17 (2007) 3538-3544.<br/>4) E.B. Secor, Principles of aerosol jet printing. Flex. Print. Electron. 3 (2018) 035002.