Min Ju Cho

Highly Photosensitive J‐Aggregated Single‐Crystalline Organic Transistors

Charge-transport phenomena and photoinduced charge generation of organic semiconductors have potential applications in many electronic and optoelectronic devices. Organic fi eld-effect transistors (OFETs) are the most promising electronic devices fabricated using either well-defi ned single crystals (SCs) or thin fi lms as the charge-transporting layers. [ 1–3 ] In particular, soluble organic semiconductors are attracting attention for use in the fabrication of low-cost, large-scale, and practical devices. [ 4 , 5 ]

High-mobility anthracene-based X-shaped conjugated molecules for thin film transistors

New anthracene-based X-shaped conjugated molecules and for use as highly soluble p-type organic semiconductors were developed and exhibited large field-effect mobilities of 0.04 cm(2) V(-1) s(-1) (I(on)/I(off) = 2.8 x 10(5)) and 0.24 cm(2) V(-1) s(-1) (I(on)/I(off) = 5.4 x 10(6)) for devices of and , respectively.

A novel tellurophene-containing conjugated polymer with a dithiophenyl diketopyrrolopyrrole unit for use in organic thin film transistors

A new tellurophene-based π-conjugated polymer, PDTDPPTe, was synthesized. PDTDPPTe exhibits a smaller optical band gap (E(g)(opt) = 1.25 eV) than thiophene-based PDTDPPT (E(g)(opt) = 1.30 eV). Thin-film transistors comprising PDTDPPTe displayed outstanding performance (μ(max) = 1.78 cm(2) V(-1) s(-1), I(on)/I(off) = 10(5-6)).

Highly sensitive phototransistor with crystalline microribbons from new π-extended pyrene derivative via solution-phase self-assembly

A new pyrene-cored π-conjugated molecule has been synthesized through Sonogashira coupling reaction. The single-crystalline microribbon-based FET exhibited the highest mobility of 0.7 cm(2) V(-1) s(-1) (I(on)/I(off) > 10(6)). Single-crystalline microribbons were employed to operate in an organic phototransistor (OPT) under very low light intensity (I = 5.6 μW cm(-2)).

Organic thin film transistors using 6,13-bis(tri-isopropylsilylethynyl)pentacene embedded into polymer binders

The active channel material of an organic thin film transistor (OTFT), 6,13-bis(tri-isopropylsilylethynyl)pentacene (TIPS pentacene), is a functionalized pentacene designed to enhance both the solubility and solid-state packing of the pentacene. In this work, in order to improve device performance, three types of polymer binders—poly(α-methylstyrene) (PAMS), poly(4-vinylbiphenyl) (PVBP), and poly(triarylamine) (PTAA)—were employed to fabricate OTFT devices with organic soluble TIPS pentacene. These binders improved film formation in a large area uniformly and helped the TIPS pentacene to form a stronger binding between source/drain electrodes onto dielectric layer. Thus, device performance was highly improved due to improvement of interfacial contact and an increase in the charge transfer in the active channel. OTFTs using TIPS pentacene with PAMS, PVBP, and PTAA for field effect mobilities in the saturation regime have 5×10−3, 8×10−3, and 2.7×10−2 cm2/V s, respectively.

High mobility isoindigo-based π-extended conjugated polymers bearing di(thienyl)ethylene in thin-film transistors

New isoindigo and di(thienyl)ethylene-containing π-extended conjugated polymers with different branched side-chains and molecular weights (MWs) have been synthesized. Octyldodecyl (OD) and decyltetradecyl (DT) groups were employed as side chain moieties tethered to isoindigo units. In addition, the MW of the polymer was varied by changing the polymerization time. The polymers bearing DT side chains showed much better charge transport behavior, compared to that of polymers with OD side chains. The hole mobility of high-MW PIIDDTE-III with DT side-chains was determined to be higher than that of the low-MW polymer, PIIDDTE-II with identical side-chains. The thermally annealed film of PIIDDTE-III exhibited outstanding hole mobilities of ∼2.20 cm2 V−1 s−1 measured under ambient conditions. This work unambiguously demonstrates the effect of the branched side-chain bulkiness and MW on the thin film transistor (TFT) performances.

Thermally activated delayed fluorescence blue dopants and hosts: from the design strategy to organic light-emitting diode applications

Thermally activated delayed fluorescence (TADF) materials have attracted much attention in the field of organic light-emitting diodes (OLEDs), with their state-of-the-art performance in terms of external quantum efficiencies (EQEs), turn-on voltages, and color coordinates. TADF materials exhibited EQEs above 25% due to harvesting both singlet and triplet excitons via reverse intersystem crossing (RISC). A small singlet–triplet energy gap (ΔEST) is essential for TADF materials to exhibit efficient upconversion from the lowest triplet excited state (T1) to the lowest singlet excited state (S1, T1 → S1). Moreover, these materials are purely organic and thus not costly. Therefore, the TADF approach provides the best alternative to conventional fluorescent and phosphorescent OLEDs, regarding device efficiency and cost. On the other hand, blue light-emitting devices are facing several issues related to their stability and efficiency, making their development quite challenging for researchers. Herein, we review the recent advances in the use of blue TADF dopants and hosts in OLEDs.

Template‐Guided Solution‐Shearing Method for Enhanced Charge Carrier Mobility in Diketopyrrolopyrrole‐Based Polymer Field‐Effect Transistors

Template-guided solution-shearing (TGSS) is used to fabricate field-effect transistors (FETs) composed of micropatterned prisms as active channels. The prisms comprise highly crystalline PTDPP-DTTE, in which diketopyrrolopyrrole (DPP) is flanked by thiophene. The FET has a maximum mobility of approximately 7.43 cm(2) V(-1) s(-1) , which is much higher than the mobility values of the thin-film transistors with solution-sheared or spin-coated films of PTDPP-DTTE annealed at 200 °C.

Semiconducting 2,6,9,10-tetrakis(phenylethynyl)anthracene derivatives: effect of substitution positions on molecular energies.

2,6-Bis((4-hexylphenyl)ethynyl)-9,10-bis(phenylethynyl)anthracene, 4, and 9,10-bis((4-hexylphenyl)ethynyl)-2,6-bis (phenyl ethynyl)anthracene, 5, have been synthesized to study their electronic and photophysical properties. It should be noted that the difference between these compounds is the substitution position of 1-ethynyl-4-hexylbenzene groups into an anthracene ring. In particular, substitution in the 9,10-positions of the anthracene ring enhanced J-aggregated intermolecular interactions. Since 5 has a lower bandgap energy and more compact film morphology, it exhibited higher hole mobility (∼0.27 cm(2) V(-1) s(-1)) in thin-film transistor devices.

Bis(thienothiophenyl) Diketopyrrolopyrrole-Based Conjugated Polymers with Various Branched Alkyl Side Chains and Their Applications in Thin-Film Transistors and Polymer Solar Cells

New thienothiophene-flanked diketopyrrolopyrrole and thiophene-containing π-extended conjugated polymers with various branched alkyl side-chains were successfully synthesized. 2-Octyldodecyl, 2-decyltetradecyl, 2-tetradecylhexadecyl, 2-hexadecyloctadecyl, and 2-octadecyldocosyl groups were selected as the side-chain moieties and were anchored to the N-positions of the thienothiophene-flanked diketopyrrolopyrrole unit. All five polymers were found to be soluble owing to the bulkiness of the side chains. The thin-film transistor based on the 2-tetradecylhexadecyl-substituted polymer showed the highest hole mobility of 1.92 cm2 V(-1) s(-1) due to it having the smallest π-π stacking distance between the polymer chains, which was determined by grazing incidence X-ray diffraction. Bulk heterojunction polymer solar cells incorporating [6,6]-phenyl-C71-butyric acid methyl ester as the n-type molecule and the additive 1,8-diiodooctane (1 vol %) were also constructed from the synthesized polymers without thermal annealing; the device containing the 2-octyldodecyl-substituted polymer exhibited the highest power conversion efficiency of 5.8%. Although all the polymers showed similar physical properties, their device performance was clearly influenced by the sizes of the branched alkyl side-chain groups.