The universal role of high-k fluorinated dielectrics in assisting the carrier transport in transistors for a broad range of printable semiconductors is explored. These results present general rules for how to design dielectric materials and achieve devices with a high carrier concentration, low disorder, reliable operation, and robust properties.

A specific design for solution‐processed doping of active semiconducting materials would be a powerful strategy in order to improve device performance in flexible and/or printed electronics. Tetrabutylammonium fluoride and tetrabutylammonium hydroxide contain Lewis base anions, F− and OH−, respectively, which are considered as organic dopants for efficient and cost‐effective n‐doping processes both in n‐type organic and nanocarbon‐based semiconductors, such as poly[[N,N′‐bis(2‐octyldodecyl)‐naphthalene‐1,4,5,8‐bis(dicarboximide)‐2,6‐diyl]‐alt‐5,5′‐(2,2′‐bithiophene)] (P(NDI2OD‐T2)) and selectively dispersed semiconducting single‐walled carbon nanotubes by π‐conjugated polymers. The dramatic enhancement of electron transport properties in field‐effect transistors is confirmed by the effective electron transfer from the dopants to the semiconductors as well as controllable onset and threshold voltages, convertible charge‐transport polarity, and simultaneously showing excellent device stabilities under ambient air and bias stress conditions. This simple solution‐processed chemical doping approach could facilitate the understanding of both intrinsic and extrinsic charge transport characteristics in organic semiconductors and nanocarbon‐based materials, and is thus widely applicable for developing high‐performance organic and printed electronics and optoelectronics devices.

Charge transport in carbon nanotube network transistors strongly depends on the properties of the gate dielectric that is in direct contact with the semiconducting carbon nanotubes. In this work, we investigate the dielectric effects on charge transport in polymer-sorted semiconducting single-walled carbon nanotube field-effect transistors (s-SWNT-FETs) by using three different polymer insulators: A low-permittivity (ε) fluoropolymer (CYTOP, ε = 1.8), poly(methyl methacrylate) (PMMA, ε = 3.3), and a high-ε ferroelectric relaxor [P(VDF-TrFE-CTFE), ε = 14.2]. The s-SWNT-FETs with polymer dielectrics show typical ambipolar charge transport with high ON/OFF ratios (up to ∼10) and mobilities (hole mobility up to 6.77 cm V s for CYTOP). The s-SWNT-FET with the lowest-k dielectric, CYTOP, exhibits the highest mobility owing to formation of a favorable interface for charge transport, which is confirmed by the lowest activation energies, evaluated by the fluctuation-induced tunneling model (FIT) and the traditional Arrhenius model (E = 60.2 meV and E = 10 meV). The operational stability of the devices showed a good agreement with the activation energies trend (drain current decay ∼14%, threshold voltage shift ∼0.26 V in p-type regime of CYTOP devices). The poor performance in high-ε devices is accounted for by a large energetic disorder caused by the randomly oriented dipoles in high-k dielectrics. In conclusion, the low-k dielectric forms a favorable interface with s-SWNTs for efficient charge transport in s-SWNT-FETs.

We report the fabrication of high-performance, printed, n-channel organic field-effect transistors (OFETs) based on an N,N-dialkyl-substituted-(1,7&1,6)-dicyanoperylene-3,4:9,10-bis(dicarboximide) derivative, PDI-RCN2, optimized by the solvent-vapor annealing (SVA) process. We performed a systematic study on the influence of solubility and the chemical structure of a solvent used for the SVA process on the ordering and orientation of PDI-RCN2 molecules in the thin film. The PDI-RCN2 film showed improved crystallinity under vapor annealing with the aliphatic 1,2-dichloroethane (DCE) as a marginal solvent. The n-type OFETs with DCE-vapor-annealed PDI-RCN2 show highly improved charge-carrier mobility of ~0.5 cm(2) V(-1) s(-1) and higher stability under gate bias stress than the pristine OFETs. This large performance improvement was mainly attributed to increased crystallinity of the semiconductor thin film, enhancing π-π stacking. We also introduced a new method to pattern crystallinity of a certain region in the semiconducting film by selective exposure to the solvent vapor using a shadow mask. The crystal-patterned PDI-RCN2 OFETs exhibit decreased off-currents by ~10× and improved gate bias stability by minimizing crosstalk, reducing leakage current between devices, and reducing the density of charge trap states of the organic semiconductor.

N-channel organic field-effect transistors (OFETs) have generally shown lower field-effect mobilities (μFET) than their p-type counterparts. One of the reasons is the energetic misalignment between the work function (WF) of commonly used charge injection electrode, i.e. gold (Au), and the lowest unoccupied molecular orbital (LUMO) of n-channel electron-transporting organic semiconductors. Here, we report barium salts as solution-processed interlayers, to improve the electron-injection and/or hole-blocking in top-gate/bottom-contact n-channel OFETs, based on poly{[N,N'-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-alt-5,5'-(2,2'-dithiophene)} (P(NDI2OD-T2)) and phenyl-C61-butyric acid methyl ester (PC61BM). Two different barium salts, barium hydroxide (Ba(OH)2) and barium chloride (Ba(Cl)2), are employed as the ultrathin interlayer (∼2 nm); and they effectively tune the WF of Au from 4.9 eV, to as low as 3.5 eV. The resulting n-channel OFETs exhibit significantly improved μFET, approaching 2.6 cm(2)/(V s) and 0.1 cm(2)/(V s) for the best P(NDI2OD-T2) and PC61BM devices, respectively, with Ba(OH)2 as interlayer.