Hui-Jun Yun

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.

Dramatic inversion of charge polarity in diketopyrrolopyrrole-based organic field-effect transistors via a simple nitrile group substitution.

A record-breaking high electron mobility of 7.0 cm(2) V(-1) s(-1) for n-channel polymer OFETs is reported. By the incorporation of only one nitrile group as an electron-withdrawing function in the vinyl linkage of the DPP-based copolymer, a dramatic inversion of majority charge-carriers from holes to electrons is achieved.

Novel Diketopyrroloppyrrole Random Copolymers: High Charge‐Carrier Mobility From Environmentally Benign Processing

The random copolymerization between two different diketopyrrolopyrole-based conducting units represents a suitable synthetic strategy to increase the solubility of polymer semiconductors in a non-chlorinated solvent, without compromising the high charge-carrier mobility. Highly performing thin-film transistors processed from environmentally benign solvents such as tetralin are demonstrated for the first time, resulting in a mobility of greater than 5 cm(2) V(-1) s(-1).

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.

Synthesis of Poly(benzothiadiazole‐co‐dithienobenzodithiophenes) and Effect of Thiophene Insertion for High‐Performance Polymer Solar Cells

We describe herein the synthesis of novel donor-acceptor conjugated polymers with dithienobenzodithiophenes (DTBDT) as the electron donor and 2,1,3-benzothiadiazole as the electron acceptor for high-performance organic photovoltaics (OPVs). We studied the effects of strategically inserting thiophene into the DTBDT as a substituent on the skeletal structure on the opto-electronic performances of fabricated devices. From UV/Vis absorption, electrochemical, and field-effect transistor analyses, we found that the thiophene-containing DTBDT derivative can substantially increase the orbital overlap area between adjacent conjugated chains and thus dramatically enhance charge-carrier mobility up to 0.55 cm(2)  V(-1)  s(-1). The outstanding charge-transport characteristics of this polymer allowed the realization of high-performance organic solar cells with a power conversion efficiency (PCE) of 5.1 %. Detailed studies on the morphological factors that enable the maximum PCE of the polymer solar cells are discussed along with a hole/electron mobility analysis based on the space-charge-limited current model.

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.

Analysis of charge transport in high-mobility diketopyrrolopyrole polymers by space charge limited current and time of flight methods

The hole mobility of the widely studied diketopyrrolopyrole-based polymers (PDPPDTSE) was examined using space charge limited current (SCLC) and time of flight (TOF) methods. The mobility of the hole-only device based on PDPPDTSE was found to be dependent upon the e-field over the range of 10−3 to 10−2 cm2 V−1 s−1 with nearly identical Poole–Frenkel coefficients. In addition, we found that the mobility strongly depended on the thickness of the PDPPDTSE. By analyzing the temperature dependence of transport characteristics, we argued that the charge transport in this polymer was greatly influenced by trap distribution at the electrode/semiconductor interface.

High-speed solution-processed organic single crystal transistors using a novel triisopropylsilylethynyl anthracene derivative

A high-quality organic single crystal transistor (OSCT) was fabricated via solution-processing using a novel anthracene derivative (TIPsAntNE). The OSCT fabricated on a surface-modified high-capacitance ZrOx substrate provided a transistor that operated at low voltages with a high mobility up to 4.1 cm2/Vs and negligible hysteresis (a Vth shift of 1 A/W) of the TIPsAntNE single crystal was high over a wide range across the visible spectrum.

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.