Switching p-type to high-performance n-type organic electrochemical transistors via doped state engineering

Abstract

High-performance n-type organic electrochemical transistors (OECTs) are essential for logic circuits and sensors. However, the performances of n-type OECTs lag far behind that of p-type ones. Conventional wisdom posits that the LUMO energy level dictates the n-type performance. Herein, we show that engineering the doped state is more critical for n-type OECT polymers. By balancing more charges to the donor moiety, we could effectively switch a p-type polymer to high-performance n-type material. Based on this concept, the polymer, P(gTDPP2FT), exhibits a record high n-type OECT performance with μC* of 54.8 F cm−1 V−1 s−1, mobility of 0.35 cm2 V−1 s−1, and response speed of τon/τoff = 1.75/0.15 ms. Calculations and comparison studies show that the conversion is primarily due to the more uniform charges, stabilized negative polaron, enhanced conformation, and backbone planarity at negatively charged states. Our work highlights the critical role of understanding and engineering polymers’ doped states.

Molecularly Hybridized Conduction in DPP‐Based Donor–Acceptor Copolymers toward High‐Performance Iono‐Electronics

“…The extracted peak intensities in select ranges (750 nm in the visible range and 1100 nm in NIR) reveal that the electrolyte is indeed able to permeate through the film bulk, oxidizing the semiconducting polymer chains, thus depleting the absorption in the visible range at the expense of the then formed polarons and bipolarons which absorb much higher wavelengths. [ 37,49 ] With increasing gT percent, the bleaching behavior and polaron/bipolaron formation showed to require much lower applied voltages (Figure 3C–F), revealing that as anticipated, the glycol‐functionalized copolymers uptake hydrated ionic species much easier than the parent DPP films. In agreement with the CV results discussed above, efficient bulk modulation was also observed when using a neat ionic liquid (EMIM TFSI) as the electrolyte (Figure 3I–L).…”

“…[32][33][34] Particularly in OECT devices, DPP-based polymers have been employed when either flanked with polar sidechains (e.g., oligoethers) or copolymerized with donor blocks bearing polar groups to attain mixed ionic electronic conduction. [29,[35][36][37] To date, these systems are among the top performers in electrochemical devices. [20,38] However, though DPP polymers continue to find use in electrochemical devices, from a molecular design viewpoint, increasing the ion uptake capabilities (maximizing the volumetric capacitance) has been the major focus.…”

High-performance n-type organic mixed ionic-electronic conductors enabled by strong cation-π interactions

“…1), confirming the high purity of the monomer. TDPP was grafted with hepta ethylene glycol methyl ether (mPEG7, R1) and branched ethylene glycol (R2) a the side chains 35,36 . The branched side chain was employed to further optimize the device performance due to its better hydrophilicity.…”

“…Thiophene-flanked diketopyrrolopyrrole (TDPP) was chosen as the building block for this study because it is cheap and has good charge transport properties due to its planar backbone 33 . However, since the LUMO energy levels of TDPP is relatively high, to date, almost all the TDPP-based conjugated polymers show p-type or ambipolar OECT behaviors 10,[34][35][36] . To build an n-type polymer based on TDPP, a copolymerized moiety with a low lying LUMO level is essential.…”

n-Type semiconductors for organic electrochemical transistor applications

“…Some p-type OECT materials could be switched to n-type OECT materials through modifications at the molecular level. In 2022, Lei's group introduced fluorine atoms on thiophene units so that p-type polymer P(gTDPPT) changed into n-type polymer P(gTDPP2FT) [90]. Calculations of the properties of the polymers' doped states showed that compared with P(gTDPPT), the negative charges of [P(gTDPP2FT)] 1-are more delocalized, leading to more balanced charge distribution on the whole polymer chain, hence [P(gTDPP2FT)] 1has better stability.…”