High-Performance All-Polymer Photodetectors Enabled by New Random Terpolymer Acceptor with Fine-Tuned Molecular Weight.

Reducing the dark current density and enhancing the overall performance of the device is the focal point in research for organic photodetectors. Two novel random terpolymers (P3 and P4) with different molecular weights are synthesized and evaluated as acceptors in bulk heterojunction (BHJ) polymer photodetectors. Compared with known acceptor materials, such as N2200 (P1) and F-N2200 (P2), polymer P4 has a lower lowest unoccupied molecular orbital (LUMO) energy level, favorable morphology, and good miscibility with a donor material J71, which leads to proper phase separation of the blend film and better dissociation of excitons and transport of carriers. Therefore, a considerably low dark current density (Jd) of 1.9 × 10-10 A/cm2 and a high specific detectivity (D*) of 1.8 × 1013 cm Hz1/2/W (also "Jones") at 580 nm under a -0.1 V bias are realized for the P4-based photodetector. More importantly, the device also exhibits a fast response speed (τr/τf = 1.24/1.87 µs) and a wide linear dynamic range (LDR) of 109.2 dB. This work demonstrates that high-performance all-polymer photodetectors with ideal morphology can be realized by random polymer acceptors with a fine-tuned molecular weight.

Advances in Organic Near-Infrared Materials and Emerging Applications.

Much progress has been made in the field of research on organic near-infrared materials for potential applications in photonics, communications, energy, and biophotonics. This account mainly describes our research work on organic near-infrared materials; in particular, donor-acceptor small molecules, organometallics, and donor-acceptor polymers with the bandgaps less than 1.2 eV. The molecular designs, structure-property relationships, unique near-infrared absorption, emission and color/wavelength-changing properties, and some emerging applications are discussed.

Fabrication of both the photoactive layer and the electrode by electrochemical assembly: towards a fully solution-processable device.

We present an economical route to achieve an all-solution and vacuum-deposition free device for fabrication of both the photoactive layer and the electrode. This low cost strategy offers a wide range of possibilities in terms of chemical and physical properties for the fabrication of tailor-made materials and their devices.

In situ switching layer-by-layer assembly: one-pot rapid layer assembly via alternation of reductive and oxidative electropolymerization.

In situ one-pot rapid layer-by-layer assembly of polymeric films as an active layer of a photoactive device via alternation of reductive and oxidative electropolymerization has been demonstrated. This novel fabrication without moving or changing experimental gears would be a powerful strategy to develop automated layer-by-layer machines.

Proton irradiation damage mechanism of PANDA-type polarization-maintaining optical fibers.

The effects of proton irradiation with energies of 3.5 and 5 MeV on the optical properties of PANDA (polarization-maintaining and absorption-reducing) optical fiber were investigated. The displacement and the ionization damage in the fiber induced by proton irradiation at 3.5, 5, and 10 MeV were calculated, respectively, using a Stopping and Range of Ions in Matter code. The irradiation-induced defects were analyzed by means of x-ray photoelectron spectroscopy, electron paramagnetic resonance, Fourier-transform infrared spectrometry, and broadband optical spectrum analysis. The results show that the proton irradiation leads to an increase of optical loss around 1310 nm and that the effect of 3.5 MeV protons is more severe than that of 5 MeV.

Solvent-tuned multiple self-assembly of a new sugar-appended gelator.

4-(4'-Butoxyphenyl)phenyl-beta-O-D-glucoside was synthesized as a low-molecular-mass gelator. It was able to immobilize a variety of aqueous and organic solvents in large amounts through the formation of three-dimensional self-assembled fibrillar networks. The morphologies of the aggregates depended on the nature of solvent where they were formed. Planar ribbons were observed in water, while helical ribbons were dominant in toluene and sheets in CHCl(3). The xerogel from water exhibited a lamellar structure with a d-spacing of 2.45 nm as demonstrated by 1D-WAXD, indicating a bilayer structure interdigitated with butoxy tails, whereas the xerogel from CHCl(3) or toluene yielded a lamellar structure with a d-spacing of 3.05 nm, implying a bilayer structure interdigitated with glycosyl heads. Increasing the content of 1,4-dioxane in water caused a gradual transformation from planar to twisted ribbons and then tubes.

Synthesis and characterization of near-infrared absorbing and fluorescent liquid-crystal chromophores.

This work demonstrates that the donor-acceptor-donor charge-transfer chromophores can be tailor-made to be near-infrared absorbing and fluorescent, as well as being liquid crystals. The chromophore containing an extremely strong acceptor of benzo[1,2-c:4,5-c']bis([1,2,5]thiadiazole) can form a columnar mesophase that absorbs at 890 nm and emits at 1160 nm in the solid state. These chromophores are readily soluble in common organic solvents and can form thin films by casting or spin coating, making them suitable for further device applications.

Efficient synthesis and properties of novel near-infrared electrochromic anthraquinone imides.

An efficient synthesis of novel near-infrared electrochromic 6-substituted (NO2, Br) anthraquinone imides, i.e., 2a and 2b, was established. Bearing functional groups suitable for further structural modifications by nucleophilic substitution reaction and various metal-catalyzed coupling reactions (e.g., Suzuki coupling), 2a and 2b were easily transferred to 1a by reaction with 4-methoxyphenol and 1b by reaction with 4-hexyloxyphenylboronic acid, respectively. These new imides are electrochromic and absorb intensely in the near-infrared range of 700-1600 nm upon electrochemical reduction.