Il Kang

Record High Hole Mobility in Polymer Semiconductors via Side-Chain Engineering

Charge carrier mobility is still the most challenging issue that should be overcome to realize everyday organic electronics in the near future. In this Communication, we show that introducing smart side-chain engineering to polymer semiconductors can facilitate intermolecular electronic communication. Two new polymers, P-29-DPPDBTE and P-29-DPPDTSE, which consist of a highly conductive diketopyrrolopyrrole backbone and an extended branching-position-adjusted side chain, showed unprecedented record high hole mobility of 12 cm(2)/(V·s). From photophysical and structural studies, we found that moving the branching position of the side chain away from the backbone of these polymers resulted in increased intermolecular interactions with extremely short π-π stacking distances, without compromising solubility of the polymers. As a result, high hole mobility could be achieved even in devices fabricated using the polymers at room temperature.

Effect of Selenophene in a DPP Copolymer Incorporating a Vinyl Group for High‐Performance Organic Field‐Effect Transistors

A new polymeric semiconductor, PDPPDTSE, is reported which is composed of a diketopyrrolopyrrole moiety and selenophenylene vinylene selenophene, with a high field-effect mobility achieved through intermolecular donor-acceptor interactions. The field-effect mobility of OFET devices based on PDPPDTSE by spin-casting is 4.97 cm(2) V(-1) s(-1) , which is higher than predecessor polymeric semiconductors.

Highly rigid and twisted anthracene derivatives: a strategy for deep blue OLED materials with theoretical limit efficiency

New highly twisted and rigid blue materials composed of anthracene with xylene as the core unit and either naphthalene or phenyl end units were synthesized. Non-doped devices using BDNA displayed 5.26% maximum external quantum efficiency with CIE color coordinates (x, y: 0.159, 0.072).

Solvent Additive to Achieve Highly Ordered Nanostructural Semicrystalline DPP Copolymers: Toward a High Charge Carrier Mobility

A facile spin-coating method in which a small percentage of the solvent additive, 1-chloronaphthalene (CN), is found to increase the drying time during film deposition, is reported. The field-effect mobility of a PDPPDBTE film cast from a chloroform-CN mixed solution is 0.46 cm(2) V(-1) s(-1). The addition of CN to the chloroform solution facilitates the formation of highly crystalline polymer structures.

A new electron transporting material for effective hole-blocking and improved charge balance in highly efficient phosphorescent organic light emitting diodes

A highly efficient new benzoimidazole phosphine oxide based electron transporting material, bis(1-phenyl-1H-benzo[d]imidazole)phenylphosphine oxide (BIPO), was designed, synthesized by condensation, nucleophilic substitution and oxidation reactions, and confirmed using various spectroscopic studies. It shows a thermal stability (ΔT5%) of 451 °C with a glass transition temperature of 129 °C from the thermogravimetric analysis and differential scanning calorimetry studies. BIPO used as an efficient electron transport layer (ETL) in a green emitting phosphorescent organic light emitting diode, ITO/4,4′-bis[N-(1-naphthyl)-N-phenyl-amino]biphenyl (30 nm)/4,4′,4′′-tris(carbazole-9-yl)triphenylamine 10 nm)/(4,4′-N,N′-dicarbazole)biphenyl (CBP) host doped with Ir(ppy)3 dopant (5%) (30 nm)/ETL (40 nm)/LiF (1 nm)/Al (100 nm), serves as an effective hole-blocking material and improves the charge balance in the device, resulting in higher device efficiencies of 22.19%, 68.3 cd A−1 and 24.4 lm W−1 with a maximum luminance of 72 080 cd m−2 compared to those (17.03%, 52.0 cd A−1 and 20.9 lm W−1 with a maximum luminance of 33 490 cd m−2) of a device using a widely used ETL, 1,3,5-tris(m-pyrid-3-yl-phenyl)benzene. These results show that the new BIPO ETL could be very useful in efficient organic light emitting diodes.

High performance ink-jet printed diketopyrrolopyrrole-based copolymer thin-film transistors using a solution-processed aluminium oxide dielectric on a flexible substrate

We report high performance, ink-jet printed diketopyrrolopyrrole-based copolymer devices consisting of a solution-processed AlOX gate dielectric on a polyimide (PI) substrate. The ink-jet printed thin-film transistors (TFTs) exhibited a field-effect mobility of 2.41 cm2 V−1 s−1 and a subthreshold swing of 65 mV dec−1. We also demonstrated a flexible, low voltage-driven inverter, exhibiting a gain of −1.81 V V−1 at a driving voltage of −1.0 V.

Novel triethylsilylethynyl anthracene-based organic semiconductors for high performance field effect transistors

A series of triethylsilylethynyl anthracene (TESAN) derivatives, end-capped with bithiophene and thienothiophene, were synthesized by Suzuki coupling. The thermal, optical, electrochemical, and crystalline properties of the TESAN derivatives were reported and correlated with charge transport behavior measured via both a thin film transistor and a single crystal transistor. The TESAN derivative substituted with bithiophene exhibited more efficient π electron delocalization over the molecule compared to the derivative substituted with fused thienothiophene, and consequently gave the highest FET mobility, 1.28 cm2 V−1 s−1, from single crystal transistors with negligible hysteresis and almost zero turn-on voltage. The discrepancy of charge carrier mobility between the thin film transistor and single crystal transistor and the solvent annealing effects are discussed in conjunction with morphological and structural analyses.

Synthesis and characterization of a new π -conjugated polymer with cyanoacrylate side chain for organic thin film transistors

AbstractA new copolymer, poly(carbazol-9-yl)phenyl)-2-cyanoacrylate)-alt-(2,2′-(1,5-bis(hexyloxy)naph thalene-2,6-diyl)dithiophene)) (PCCNT) with cyanoacrylate, was synthesized by the Stille coupling reaction for p-type semiconductors in OTFTs. FTIR and 1H NMR spectroscopes confirmed the structure of PCCNT. The molecular weight of polymer was 14.6 kDa with polydispersity index of 1.72 using GPC. The obtained polymer with long alkyl side chains demonstrated good solubility. PCCNT has good thermal stability of (Td=324) as well as good oxidation stability with a HOMO level of −5.35 eV. UV-Vis absorption maximum of the polymer was found at 431 nm in solution and at 444 nm for the film, respectively. In the photoluminescence (PL), the large red-shift was observed from solution emission (λmax 493 nm) to film emission (λmax 539 nm) due to an intermolecular interaction. The fabricated bottom gate-top contact organic thin film transistors (OTFTs) showed field-effect mobility of 9.02×10−5 cm2/Vs and threshold voltage of −3 V.

Charge transport characteristics of a high-mobility diketopyrrolopyrrole-based polymer

In this study, we attempt to unveil the charge-transport abnormality of the widely studied diketopyrrolopyrrole (DPP)-based polymers with exceptionally high charge carrier mobility [>5 cm(2) V(-1) s(-1)]. Based on the electric field and temperature dependence of the charge-transport characteristics of the field effect transistor (FET) geometry of one of the highly conductive DPP derivatives, namely, (poly[2,5-bis(7-decylnonadecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-(E)-(1,2-bis(5-(thiophen-2-yl)selenophen-2-yl)ethene) (PDPPDTSE), we show that the high gate-source bias drew the carriers closer to the interface of the semiconductor/dielectric layers where the density of state (DOS) of the charge carrier is significantly broader than the bulk. We argue that the intrinsically narrow DOS in the PDPPDTSE bulk resulted in significantly different charge-transport behavior between the semiconductor bulk and the semiconductor/dielectric interface, which was not visible in the other low-mobility organic semiconductors that contain intrinsically high density of trap states in their bulk. To avoid these charge transport abnormalities, we try to operate the FETs under low gate bias without compromising the accumulated charge carrier density. By carefully employing a thin metal oxide covered with a self-assembled monolayer (SAM) as a dielectric layer, we can demonstrate low-voltage PDPPDTSE FETs with near-ideal performance both in terms of hysteresis-free operation and operating reliability while maintaining a high charge carrier mobility of ~2.8 cm(2) V(-1) s(-1).

Non-volatile hybrid memory devices with excellent reliability

Electronic applications of organic–inorganic hybrids in which both components contribute to critical functionality have offered enhanced performance over their individual components. In this work, highly reliable non-volatile memory transistors were demonstrated using a polymeric semiconductor and a floating gate consisting of PbS nanocrystals (NCs). Poly[2,5-bis(2-octyldodecyl)pyrrolo[3,4-c]pyrrole-1,4(2H,5H)-dione-(E)-1,2-di(2,2′-bithiophen-5-yl)ethene](PDPPDBTE), used as a semiconductor layer, enabled superior reliability of electronic characteristics. The fabricated unit field effect transistors revealed excellent storage stability for more than several months, long time-operational stability and bias stress durability with little change of the threshold voltage (ΔVth) (∼0.5 V) during a period of prolonged bias stress under ambient conditions. Based on the optimized transistor geometry, memory devices were constructed by embedding a layer of NCs between layers of SiO2 and CytopTM as a floating gate. The resulting memory devices revealed non-volatile memory operation with a memory on–off ratio higher than 103 and a memory window of 20 V at 30 V of writing and erasing voltage. More importantly, it turned out that the entire trapping mechanisms of the memory device originate solely from NCs, due to the inert nature of PDPPDBTE and CytopTM. As a result, very reproducible memory operation under repeated write/erase cycles for 100 times as well as long retention time of the memory state, more than 10 days were observed in ambient conditions. Detailed analyses on the physical origin of such excellent device reliability were fully discussed.