Synthesis and characterization of a new poly(octathiophene) based copolymer for organic thin-film transistor.

A new poly(octathiophene) based copolymer was designed and synthesized by the palladium catalyzed Suzuki coupling reaction. The structure of the newly obtained copolymer was confirmed by 1H-NMR and IR. The number-average molecular weight (M(n)) of the polymer was 36,000 with a poly-dispersity index of 1.15. The polymer has good solubility in common solvents such as chloroform, toluene, chlorobenzene, dichlorobenzene and tetrahydrofuran at room temperature. The optical, thermal and electrochemical properties of the polymer were characterized by UV-vis absorption, TGA and DSC and cyclovoltametry, respectively. A thin film transistor using the new polymer as an organic semiconductor was found to exhibit typical p-channel FET characteristics with a hole mobility of 5 x 10(-4) cm2/Vs.

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.

Deep-blue phosphorescence from perfluoro carbonyl-substituted iridium complexes.

The new deep-blue iridium(III) complexes, (TF)2Ir(pic), (TF)2Ir(fptz), (HF)2Ir(pic), and (HF)2Ir(fptz), consisting of 2',4″-difluororphenyl-3-methylpyridine with trifluoromethyl carbonyl or heptafluoropropyl carbonyl at the 3' position as the main ligand and a picolinate or a trifluoromethylated-triazole as the ancillary ligand, were synthesized and characterized for applications in organic light-emitting diodes (OLEDs). Density function theory (DFT) calculations showed that these iridium complexes had a wide band gap, owing to the introduction of the strong electron withdrawing perfluoro carbonyl group. Time-dependent DFT (TD-DFT) calculations suggested that their lowest triplet excited state was dominated by a HOMO → LUMO transition and that the contribution of the metal-to-ligand charge transfer (MLCT) was higher than 34% for all four complexes, indicating that strong spin-orbit coupling exists in the complexes. The 10 wt % (TF)2Ir(pic) doped 9-(3-(9H-carbazole-9-yl)phenyl)-3-(dibromophenylphosphoryl)-9H-carbazole (mCPPO1) film exhibited the highest photoluminescence quantum yield of 74 ± 3% among the films based on the four complexes. Phosphorescent OLEDs based on (TF)2Ir(pic) and (TF)2Ir(fptz) exhibited maximum external quantum efficiencies of 17.1% and 8.4% and Commission Internationale de l'Eclairage (CIE) coordinates of (0.141, 0.158) and (0.147, 0.116), respectively. These CIE coordinates represent some of the deepest blue emissions ever achieved from phosphorescent OLEDs with considerably high EQEs.

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.

Synthesis and Characterization of New Poly(silole-fluorene) Copolymers.

New poly(silole-fluorene) copolymers were designed and synthesized. Copolymers were obtained by Suzuki coupling reaction with different ratio of fluorene and silole. The obtained copolymers were characterized by the spectroscopic methods such as FT-IR and 1H-NMR spectroscopies. The resulting copolymers were soluble in common organic solvents such as toluene, tetrahydrofurane, chloroform, chlorobenzene, etc. The obtained copolymers showed thermal stabilities, which were characterized by TGA and DSC. PLEDs with device configurations of ITO/PEDOT:PSS/Copolymer I~VI/LiF/AI. The best device performances, with maximum brightness of 231.5 cd/m2 at a current density (J) of 408.3 mA/cm2, and a maximum luminance efficiency of 0.115 cd/A, were achieved in the composition of fluorene and silole moiety (0.9:0.1).

Polarity engineering of conjugated polymers by variation of chemical linkages connecting conjugated backbones.

The fine tuning of the dominant polarity in polymer semiconductors is a key issue for high-performance organic complementary circuits. In this paper, we demonstrate a new methodology for addressing this issue in terms of molecular design. In an alternating conjugated donor-acceptor copolymer system, we systematically engineered the chemical linkages that connect the aromatic units in donor moieties. Three donor moieties, thiophene-vinylene-thiophene (TVT), thiophene-acetylene-thiophene (TAT), and thiophene-cyanovinylene-thiophene (TCNT), were combined with an acceptor moiety, thienoisoindigo (TIID), and finally, three novel TIID-based copolymers were synthesized: PTIID-TVT, PTIID-TAT, and PTIID-TCNT. We found that the vinylene, acetylene, and cyanovinylene linkages decisively affect the energy structure, molecular orbital delocalization, microstructure, and, most importantly, the dominant polarity of the polymers. The vinylene-linked PTIID-TVT field-effect transistors (FETs) exhibited intrinsic hole and electron mobilities of 0.12 and 1.5 × 10(-3) cm(2) V(-1 )s(-1), respectively. By contrast, the acetylene-linked PTIID-TAT FETs exhibited significantly improved intrinsic hole and electron mobilities of 0.38 and 0.03 cm(2) V(-1) s(-1), respectively. Interestingly, cyanovinylene-linked PTIID-TCNT FETs exhibited reverse polarity, with hole and electron mobilities of 0.07 and 0.19 cm(2) V(-1) s(-1). As a result, the polarity balance, which is quantified as the electron/hole mobility ratio, was dramatically tuned from 0.01 to 2.7. Our finding demonstrates a new methodology for the molecular design of high-performance organic complementary circuits.

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).

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.

Synthesis of a low-bandgap fluorinated donor-acceptor copolymer and its optoelectronic application.

We demonstrate the synthesis of a new copolymer which is composed of dialkyl thienylated benzodithiophene and perfluororalkyl-carbonyl thienothiophene (DTBDT-TTFO) and the characterization of its optoelectronic properties. The introduction of thienyl groups enabled the extended delocalization of π electrons in the DTBDT-TTFO backbone and efficient intermolecular charge transport as proved by the fairly high field effect mobility of 0.02 cm(2)/(V s). The introduction of perfluororalkyl-carbonyl side chains resulted in a significant red-shift of DTBDT-TTFO in the absorption spectra and a decrease in the HOMO and LUMO levels. The resulting energy levels of DTBDT-TTFO were not satisfactory for solar cell applications, especially in terms of charge separation at the polymer/PCBM interfaces. Rather, the DTBDT-TTFO showed better energy level matching with the colloidal nanocrystals (NCs) of CdSe. A photodetector based on the bulkheterojunction of DTBDT-TTFO and CdSe NCs with coplanar device geometry resulted in a high photoconductive gain (responsivity higher than 1A/W under a low operating voltage of 1 V), possibly arising from electron trapping at CdSe NCs such that the hole can travel along the detector and its surrounding circuit. More importantly, the photodetector revealed a time constant of a few hundreds of microseconds, which means that the response speed of the photodetector is fast enough for lag-free imaging applications.

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.

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.