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Two small molecules named PI-DPP and NI-DPP with a DPP core as the central strong acceptor unit and phthalimide/naphthalimide as the terminal weak acceptor were designed and synthesized. The effects of terminal phthalimide/naphthalimide units on the thermal behavior, optical and electrochemical properties, as well as the photovoltaic performance of these two materials were systematically studied. Cyclic voltammetry revealed that the lowest unoccupied molecular orbitals (LUMO) (~ -3.6 eV) of both molecules were intermediate to common electron donor (P3HT) and acceptor (PCBM). This indicated that PI-DPP and NI-DPP may uniquely serve as electron donor when blended with PCBM, and as electron acceptor when blended with P3HT, where sufficient driving forces between DPPs and PCBM, as well as between P3HT and DPPs should be created for exciton dissociation. Using as electron donor materials, PI-DPP and NI-DPP devices exhibited low power conversion efficiencies (PCEs) of 0.90% and 0.76% by blending with PCBM, respectively. And a preliminary evaluation of the potential of the NI-DPP as electron acceptor material was carried out using P3HT as a donor material, and P3HT:NI-DPP device showed a PCE of 0.6%, with an open circuit voltage (VOC) of 0.7 V, a short circuit current density (JSC) of 1.91 mA•cm-2, and a fill factor (FF) of 45%.

P-type and n-type top-gate carbon nanotube thin-film transistors (TFTs) can be selectively and simultaneously fabricated on the same polyethylene terephthalate (PET) substrate by tuning the types of polymer-sorted semiconducting single-walled carbon nanotube (sc-SWCNT) inks, along with low temperature growth of HfO2 thin films as shared dielectric layers. Both the p-type and n-type TFTs show good electrical properties with on/off ratio of ≈105 , mobility of ≈15 cm2 V-1 s-1 , and small hysteresis. Complementary metal oxide semiconductor (CMOS)-like logic gates and circuits based on as-prepared p-type and n-type TFTs have been achieved. Flexible CMOS-like inverters exhibit large noise margin of 84% at low voltage (1/2 Vdd = 1.5 V) and maximum voltage gain of 30 at Vdd of 1.5 V and low power consumption of 0.1 μW. Both of the noise margin and voltage gain are one of the best values reported for flexible CMOS-like inverters at Vdd less than 2 V. The printed CMOS-like inverters work well at 10 kHz with 2% voltage loss and delay time of ≈15 μs. A 3-stage ring oscillator has also been demonstrated on PET substrates and the oscillation frequency of 3.3 kHz at Vdd of 1 V is achieved.

Wurtzite Cu2 ZnSnS4 (WZ-CZTS) has been controllably synthesized through a hot-injection route. The crystal-growth mechanism of WZ-CZTS has been investigated by using time-dependent XRD patterns, TEM images, and absorption spectra analysis, and revealed that WZ-CZTS nucleated and grew from monoclinic Cu7 S4 nanocrystals through phase transformation of Cu7 S4 to WZ-CZTS within 5 min. The synthesis processes are dependent on precursor concentration, reaction temperature, reaction time, organic ligand, and sulfur source and have been studied in detail. It was revealed that the width of the WZ-CZTS nanocrystals was mainly controlled by the precursor concentration, which determines the diameter of Cu7 S4 . The length could be regulated by the ratio of dodecanethiol (DDT) to oleylamine (OLA) and reaction time.

The synthesis of generational dendritic oligothiophenes (DOTs) has been successfully achieved by a divergent/convergent approach that involves halogenation, boronation, and palladium-catalyzed Suzuki coupling reactions. The key point in the presented synthetic approach is the use of trimethylsilyl (TMS) protecting groups, which allow for the core-lithiation and subsequent boronation of the dendrons and for the peripheral ipso-substitution with iodine monochloride or N-bromosuccimide. In addition, the TMS protecting groups can be completely removed by using tetrabutylammonium fluoride, thus yielding only-thiophene-based dendrons and dendrimers. Due to their highly branched structure, all these synthesized DOTs are soluble in organic solvents. Chemical structures were confirmed by NMR spectroscopic, mass spectrometric, and elemental analysis. Concentration-dependent (1)H NMR spectroscopic investigations revealed that the higher generation compounds tend to aggregate in solution. Such an aggregation behavior was further confirmed by measuring with MALDI-TOF MS. Both MALDI-TOF MS and gel-permeation chromatography (GPC) analyses confirmed the monodispersity of the DOTs. Furthermore, GPC results revealed that these DOT molecules adopt a condensed globular molecular shape. Their optical and electronic properties were also investigated. The results indicated that these DOTs comprise various conjugated α-oligothiophenes with different chain lengths, which results in the higher generation compounds showing broad and featureless UV/Vis absorption spectra and ill-defined redox waves.

An excellent hole-transport material, 1, 3-diphenyil-5-(9-phenanthryl)-2-pyrazoline (DPPhP) for OLEDs was studied. This compound not only offers high glass transition temperature (Tg = 96 °C), good film forming ability, and high HOMO energy level, but also displays excellent hole-transport property. The electroluminescent device with a simple structure of ITO/DPPhP (60 nm)/AlQ (60 nm)/LiF (0.8 nm)/Al shows an external quantum efficiency as high as 1.6%.

The organization of organic semiconductor molecules in the active layer of organic electronic devices has important consequences to overall device performance. This is due to the fact that molecular organization directly affects charge carrier mobility of the material. Organic field-effect transistor (OFET) performance is driven by high charge carrier mobility while bulk heterojunction (BHJ) solar cells require balanced hole and electron transport. By investigating the properties and device performance of three structural variations of the fluorenyl hexa-peri-hexabenzocoronene (FHBC) material, the importance of molecular organization to device performance was highlighted. It is clear from 1H NMR and 2D wide-angle X-ray scattering (2D WAXS) experiments that the sterically demanding 9,9-dioctylfluorene groups are preventing π-π intermolecular contact in the hexakis-substituted FHBC 4. For bis-substituted FHBC compounds S and 6, π-π intermolecular contact was observed in solution and hexagonal columnar ordering was observed in solid state. Furthermore, in atomic force microscopy (AFM) experiments, nanoscale phase separation was observed in thin films of FHBC and [6,6]phenyl-C61-butyric acid methyl ester (FC61BM) blends. The differences in molecular and bulk structural features were found to correlate with OFET and BHJ solar cell performance. Poor OFET and BHJ solar cells devices were obtained for FHBC compound 4 while compounds 5 and 6 gave excellent devices. In particular, the field-effect mobility of FHBC 6, deposited by spincasting, reached 2.8 x 10 3Cm2 V-1 s and a power conversion efficiency of 1.5% was recorded for the BHJ solar cell containing FHBC 6 and PC 61BM. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA.

A novel family of soluble conjugated dendritic oligothiophenes (DOTs) as monodisperse 3D macromolecular architectures was characterized with respect to optical and redox properties in solution and in solid films. Band gaps of 2.5-2.2 eV, typical for organic semiconductors, were determined as well as HOMO/LUMO energy levels ideal for efficient electron transfer to acceptors such as [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) identifying them as suitable materials for solar cell applications. Solution-processed bulk-heterojunction solar cells using DOTs as electron donor and PCBM as acceptor were prepared and investigated. High open-circuit voltages V oc of 1.0 V and power-conversion efficiencies up to 1.72% were obtained for the DOT-based devices. The higher generations DOTs provide the highest efficiencies. Based on the monodispersity of the DOTs, an analysis of the molar ratio between donor and acceptor in the blended film was possible leading to an optimal value of five to six thiophene units per PCBM.

By using pyran-containing donor-acceptor dyes as doping molecules in organic light-emitting devices (OLEDs), we scrutinize the effects of charge trapping and polarization induced by the guest molecules in the electro-active host material. Laser dyes 4-(dicyanomethylene)-2-methyl-6-[2-[(julolidin-9-yl)phenyl]ethenyl]-4H-pyran (DCM2) and the novel 4-(dicyanomethylene)-2-methyl-6-[2-[(4-diphenylamino)phenyl]ethenyl]-4H-pyran (DCM-TPA) are used as model compounds. The emission color of these polar dyes depends strongly on doping concentration, which we have attributed to polarization effects induced by the doping molecules themselves. Their frontier orbital energy levels are situated within the bandgap of the tris(8-hydroxyquinoline)aluminum (Alq3) host matrix and allow the investigation of either electron trapping or both electron and hole trapping. In the case of DCM-TPA doping, we were able to show that electron trapping leads to a partial shift of the recombination zone out of the doped Alq3 region. To impede charge-recombination processes taking place in the undoped host matrix, a charge-blocking layer efficiently confines the recombination zone inside the doped zone and gives rise to increased luminous efficiency. For a doping concentration of 1 wt.-% we obtain a maximum luminous efficiency of 10.4 cd A-1. At this doping concentration, the yellow emission spectrum shows excellent color saturation with CIE chromaticity coordinates x, y of 0.49 and 0.50, respectively. In the case of DCM2 the recombination zone is much less affected for the same doping concentrations, which is ascribed to the fact that both electrons and holes are being trapped. The experimental findings are corroborated with a numerical simulation of the doped multilayer devices

Selective dispersion of semiconducting single walled carbon nanotubes (s-SWCNTs) by conjugated polymer wrapping is recognized as the most promising scalable method for s-SWCNT separation. Despite a number of linear conjugated polymers being reported for use in s-SWCNT separation, these linear polymers suffer batch-to-batch variation for their undefined molecular structure. Here, it is reported that conjugated dendritic oligothiophenes with multiple diketopyrrolopyrrole groups at the periphery have the capability of selectively dispersing large diameter s-SWCNTs with high dispersion efficiency and certain chiral selectivity. Printed top-gated thin film transistors using the dendrimer sorted s-SWCNTs show high charge carrier mobility of up to 57 cm2 V−1 s−1 and on/off ratios of ≈106 with high reproducibility, which is ascribed to the defined and monodispersed molecular structure of dendrimers. Moreover, owing to the multiple peripheral anchoring groups of these dendritic molecules, these dendrimer-s-SWCNT dispersions display excellent stability. The current work proves that dendritic molecules are excellent dispersion reagents for s-SWCNT separation.