Dongyoon Khim

Remarkable Enhancement of Hole Transport in Top‐Gated N‐Type Polymer Field‐Effect Transistors by a High‐k Dielectric for Ambipolar Electronic Circuits

A remarkable enhancement of p-channel properties is achieved in initially n-channel dominant ambipolar P(NDI2OD-T2) organic field-effect transistors (OFETs) by the use of the fluorinated high-k dielectric P(VDF-TrFE). An almost two orders of magnitude increase in hole mobility (~0.11 cm(2) V(-1) s(-1) ) originates from a strong interface modification at the semiconductor/dielectric interface, which provides high-performance complementary-like inverters and ring oscillator circuits.

Charge Injection Engineering of Ambipolar Field-Effect Transistors for High-Performance Organic Complementary Circuits

Ambipolar π-conjugated polymers may provide inexpensive large-area manufacturing of complementary integrated circuits (CICs) without requiring micro-patterning of the individual p- and n-channel semiconductors. However, current-generation ambipolar semiconductor-based CICs suffer from higher static power consumption, low operation frequencies, and degraded noise margins compared to complementary logics based on unipolar p- and n-channel organic field-effect transistors (OFETs). Here, we demonstrate a simple methodology to control charge injection and transport in ambipolar OFETs via engineering of the electrical contacts. Solution-processed caesium (Cs) salts, as electron-injection and hole-blocking layers at the interface between semiconductors and charge injection electrodes, significantly decrease the gold (Au) work function (∼4.1 eV) compared to that of a pristine Au electrode (∼4.7 eV). By controlling the electrode surface chemistry, excellent p-channel (hole mobility ∼0.1-0.6 cm(2)/(Vs)) and n-channel (electron mobility ∼0.1-0.3 cm(2)/(Vs)) OFET characteristics with the same semiconductor are demonstrated. Most importantly, in these OFETs the counterpart charge carrier currents are highly suppressed for depletion mode operation (I(off) < 70 nA when I(on) > 0.1-0.2 mA). Thus, high-performance, truly complementary inverters (high gain >50 and high noise margin >75% of ideal value) and ring oscillators (oscillation frequency ∼12 kHz) based on a solution-processed ambipolar polymer are demonstrated.

Simple Bar‐Coating Process for Large‐Area, High‐Performance Organic Field‐Effect Transistors and Ambipolar Complementary Integrated Circuits

Large-area polymer FET arrays and integrated circuits (ICs) are successfully demonstrated via a simple wire-bar-coating process. Both a highly crystalline conjugated polymer layer and very smooth insulating polymer layer are formed by a consecutive wire-bar-coating process on a 4-inch plastic substrate with a short processing time for application as the active and dielectric layers of OFET arrays and ICs.

Precisely Controlled Ultrathin Conjugated Polymer Films for Large Area Transparent Transistors and Highly Sensitive Chemical Sensors

A uniform ultrathin polymer film is deposited over a large area with molecularlevel precision by the simple wire-wound bar-coating method. The bar-coated ultrathin films not only exhibit high transparency of up to 90% in the visible wavelength range but also high charge carrier mobility with a high degree of percolation through the uniformly covered polymer nanofibrils. They are capable of realizing highly sensitive multigas sensors and represent the first successful report of ethylene detection using a sensor based on organic field-effect transistors.

Flexible Complementary Logic Gates Using Inkjet-Printed Polymer Field-Effect Transistors

High-performance inkjet-printed top-gate/bottom-contact organic field-effect transistors (OFETs) and complementary electronic circuitry are reported. Blends of poly(vinylidenefluoride-trifluoroethylene) (P(VDF-TrFE)) and poly(methyl methacrylate) (PMMA) dielectrics effectively reduce the operation voltage. At the optimized blend ratio of 7 : 3 wt.% for P(VDF-TrFE) and PMMA, both p- and n-type printed OFETs show well-balanced high field-effect mobility values (~ 0.5 cm2/V·s) and low threshold voltages ( ±5 V). The high-performance inverters and various digital logic gates such as nand, nor, or, and xor are demonstrated on flexible plastic substrates. The inverter shows a high gain (>; 25), an ideal inverting voltage near half of the supplied bias (1/2VDD), and a high noise immunity (up to 79 % of 1/2VDD).

High Performance and Stable N-Channel Organic Field-Effect Transistors by Patterned Solvent-Vapor Annealing

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.

Spray-printed organic field-effect transistors and complementary inverters

We report the fabrication of high-performance organic field-effect transistors (OFETs) and complementary inverters using spray-printed films of n-type small-molecule semiconductors and p-type conjugated polymers. Highly crystalline organic semiconductor films could be obtained by controlling the droplet size, nozzle-to-substrate distance, and solvent drying speed during the printing process. After the optimisation of the spray-printing process, the performances of the spray-printed OFETs were comparable to those of spin-coated and inkjet-printed OFETs. In addition to excellent device-to-device uniformity, the spray-printed n- and p-channel OFETs also exhibited high field-effect mobilities, which were ∼0.3 (ActivInk™ N1450, Polyera), ∼0.01 (regioregular-poly(3-hexylthiophene) (rr-P3HT)), and ∼0.25 cm2 V−1 s−1 (ActivInk™ P2100, Polyera). Organic complementary inverters were fabricated by spray printing and shadow-mask patterning while using ActivInk™ N1450 and P2100 as the n- and p-type semiconductors, respectively. The complementary inverters exhibited a large voltage gain (∼17) and a low power consumption (∼0.02 mW) at VDD = 60 V.

Organic Nano-Floating-Gate Memory with Polymer:[6,6]-Phenyl-C61 Butyric Acid Methyl Ester Composite Films

Here, we report on a pentacene-based, nonvolatile transistor memory device with poly(4-vinyl phenol) (PVP):[6,6]-phenyl-C61 butyric acid methyl ester (PCBM) nano-composite films as the charge storage site. Incorporation of PCBM molecules into PVP dielectric materials as charge storage sites for electrons resulted in a reversible shift in the threshold voltage (VTh) and reliable memory characteristics. The characteristics of the pentacene memory device were as follows: a relatively high field-effect mobility (µFET) (0.2–0.3 cm2 V-1 s-1) with a large memory window (ca. 20 V), a high on/off ratio (~104) during writing and erasing with application of an operating gate voltage of 60 V for a short duration time (~1 ms), and a retention time of about 40 h.

Large Enhancement of Carrier Transport in Solution-Processed Field-Effect Transistors by Fluorinated Dielectric Engineering

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.

Synthesis and Photovoltaic Properties of a Thienylenevinylene and Diketopyrrolopyrrole Copolymer with High Mobility

A novel donor-acceptor-type polymer with a low band-gap that alternates electron-rich thienylenevinylene groups with electron-deficient diketopyrrolopyrrole (DPP) units (PETVTDPP) has been synthesized by Pd-catalyzed Stille cross-coupling polymerization. The polymer shows a broad absorption band of wavelengths that range from 330 to 900 nm, and a low band-gap value of 1.43 eV. The field-effect mobility of an organic thin-film transistor based on this polymer is 0.05 cm(2 ) · Vs(-1) . Bulk-heterojunction solar cells using a mixture of PETVTDPP and PC[71] BM for the active layer show a power conversion efficiency (PCE) of 1.94% under simulated AM 1.5 G solar irradiation at 100 mW · cm(-2) .