9 research outputs found
Thermally Stable Zinc Disalphen Macrocycles Showing Solid-State and Aggregation-Induced Enhanced Emission
In order to investigate
the solid-state light emission of zinc salphen macrocycle complexes,
7 dinuclear zinc salphen macrocycle complexes (<b>1–7</b>), with acetate or hexanoate coligands, are synthesized. The complexes
are stable in air up to 300 °C, as shown via thermogravimetric
analysis (TGA), and exhibit green to orange-red emission in solution
(λ<sub>em</sub> = 550–600 nm, PLQE ≤ 1%) and slightly
enhanced yellow to orange-red emission in the solid state (λ<sub>em</sub> = 570–625 nm, PLQE = 1–5%). Complexes <b>1</b>, <b>2</b>, <b>4</b>, <b>5</b>, and <b>7</b> also display aggregation-induced enhanced emission (AIEE)
when hexane (a nonsolvent) is added to a chloroform solution of the
complexes, with complex <b>4</b> displaying a 75-fold increase
in peak emission intensity upon aggregation (in 0.25:0.75 chloroform:hexane
mixture)
Confined Surface Plasmon–Polariton Amplifiers
We
demonstrate the realization of confined surface plasmon polariton
amplifiers using a thin layer of the organic gain medium 4-dicyanomethylene-2-methyl-6-(<i>p</i>-dimethylaminostyryl)-4<i>H</i>-pyran dispersed
in a tris(8-hydroxy-quinolinato)aluminum matrix. Complete loss compensation,
which occurs at a pump fluence of approximately 200 μJ/cm<sup>2</sup>, is directly observed in the time domain and studied for
a range of waveguide lengths. The power dependence is also reported,
and a significant net gain of 93 dB/mm is observed at the highest
fluence
Thickness Effect of Bulk Heterojunction Layers on the Performance and Stability of Polymer:Fullerene Solar Cells with Alkylthiothiophene-Containing Polymer
We
report a pronounced thickness effect of bulk heterojunction
(BHJ) layers on the performance and stability of inverted polymer
solar cells with the BHJ layers of poly[(4,8-bis(5-(octylthio)thiophen-2-yl)benzo[1,2-b:4,5-b′]dithiophene-<i>co</i>-3-fluorothieno[3,4- b]thiophene-2-carboxylate]
(PBDT-TS1) and [6,6]-phenyl-C<sub>71</sub>-butyric acid methyl ester
(PC<sub>71</sub>BM). The thickness of the BHJ layers was varied from
40 to 120 nm by changing solution concentrations and spin-coating
speeds. The results showed that the film thickness considerably affected
the performance and stability of devices. The power conversion efficiency
reached ca. 9% at the thickness of 80 nm by the optimized nanoscale
phase separation between donor and acceptor components. However, the
devices with 120 nm-thick BHJ layers showed better device stability
under continuous illumination with a simulated solar light due to
the well-maintained surface morphology and nanostructure in addition
to the improved morphological volume stability
Efficient Deep Red Light-Sensing All-Polymer Phototransistors with <i>p</i>‑type/<i>n</i>-type Conjugated Polymer Bulk Heterojunction Layers
Here
we demonstrate deep red light-sensing all-polymer phototransistors
with bulk heterojunction layers of poly[4,8-bis[(2-ethylhexyl)-oxy]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-<i>b</i>]-thiophenediyl] (PTB7) and poly[[<i>N</i>,<i>N</i>′-bis(2-octyldodecyl)-naphthalene-1,4,5,8-bis(dicarboximide)-2,6-diyl]-<i>alt</i>-5,5′-(2,2′-bithiophene)] (P(NDI2OD-T2)).
The device performances were investigated by varying the incident
light intensity of the deep red light (675 nm), while the signal amplification
capability was examined by changing the gate and drain voltages. The
result showed that the present all-polymer phototransistors exhibited
higher photoresponsivity (∼14 A/W) and better on/off photoswitching
characteristics than the devices with the pristine polymers under
illumination with the deep red light. The enhanced phototransistor
performances were attributed to the well-aligned nanofiber-like morphology
and nanocrystalline P(NDI2OD-T2) domains in the blend films, which
are beneficial for charge separation and charge transport in the in-plane
direction
Dependence of Charge Separation Efficiency on Film Microstructure in Poly(3-hexylthiophene-2,5-diyl):[6,6]-Phenyl-C<sub>61</sub> Butyric Acid Methyl Ester Blend Films
Herein we address the factors controlling photocurrent generation in P3HT:PCBM blend films as a function of blend composition and annealing treatment. Absorption, photoluminescence, and transient absorption spectroscopy are used to distinguish the role of exciton dissociation, charge pair separation, and charge collection. Variations in blend film microstructure with composition and annealing treatment are studied using X-ray diffraction. While the trend in photocurrent generation with composition and annealing [Muller, et al., <i>Adv. Mater.</i> <b>2008</b>, <i>20</i>, 3510] does not follow the trend in exciton dissociation, it closely follows the trend in charge pair generation. Moreover, charge pair generation efficiency is positively correlated to the degree of polymer crystallization and the appearance of large domains of both polymer and fullerene phases. We argue that larger domains assist charge pair separation by increasing the probability of escape from the P3HT:PCBM interface, thus reducing geminate charge recombination
Competition between the Charge Transfer State and the Singlet States of Donor or Acceptor Limiting the Efficiency in Polymer:Fullerene Solar Cells
We study the appearance and energy of the charge transfer
(CT)
state using measurements of electroluminescence (EL) and photoluminescence
(PL) in blend films of high-performance polymers with fullerene acceptors.
EL spectroscopy provides a direct probe of the energy of the interfacial
states without the need to rely on the LUMO and HOMO energies as estimated
in pristine materials. For each polymer, we use different fullerenes
with varying LUMO levels as electron acceptors, in order to vary the
energy of the CT state relative to the blend with [6,6]-phenyl C61-butyric
acid methyl ester (PCBM). As the energy of the CT state emission approaches
the absorption onset of the blend component with the smaller optical
bandgap, <i>E</i><sub>opt,min</sub> ≡ min{<i>E</i><sub>opt,donor</sub>; <i>E</i><sub>opt,acceptor</sub>}, we observe a transition in the EL spectrum from CT emission to
singlet emission from the component with the smaller bandgap. The
appearance of component singlet emission coincides with reduced photocurrent
and fill factor. We conclude that the open circuit voltage <i>V</i><sub>OC</sub> is limited by the smaller bandgap of the
two blend components. From the losses of the studied materials, we
derive an empirical limit for the open circuit voltage: <i>V</i><sub>OC</sub> ≲ <i>E</i><sub>opt,min</sub>/<i>e</i> – (0.66 ± 0.08)eV
Steric-Hindrance-Functionalized Polydiarylfluorenes: Conformational Behavior, Stabilized Blue Electroluminescence, and Efficient Amplified Spontaneous Emission
Control
of the hierarchical molecular organization of polydiarylfluorenes
by synthetic strategies is significant for optimizing photophysical
properties as well as the performance of light-emitting devices. Herein,
for the suppression of molecular aggregation and enhancement of luminescence
efficiency, a series of steric units were introduced into polydiarylfluorenes
by copolymerization, with the aim of integrating the advantages of
the steric-hindrance effect and of the β-phase. Optical and
Raman spectroscopies revealed a β-phase conformation for a polymer
copolymerized with spiro[fluorene-9,9′-xanthene] (SFX), with
photoluminescence (PL) peaks at 454, 482, and 517 nm. Moreover, the
morphological stability and electroluminescence (EL) stability were
also improved without compromising the performance of the polymer
light-emitting diodes (PLEDs). Furthermore, three steric-hindrance-functionalized
copolymers showed significantly decreased thresholds for amplified
spontaneous emission (<i>E</i><sub>th</sub><sup>ASE</sup>) and enhanced stability following thermal annealing treatment. These
results indicate that steric-hindrance functionalization is a superior
approach to improve the overall stability and optoelectronic properties
for blue-light-emitting π-conjugated polymers
Photophysical and Fluorescence Anisotropic Behavior of Polyfluorene β‑Conformation Films
We
demonstrate a systematic visualization of the unique photophysical
and fluorescence anisotropic properties of polyfluorene coplanar conformation
(β-conformation) using time-resolved scanning confocal fluorescence
imaging (FLIM) and fluorescence anisotropy imaging microscopy (FAIM)
measurements. We observe inhomogeneous morphologies and fluorescence
decay profiles at various micrometer-sized regions within all types
of polyfluorene β-conformational spin-coated films. Poly(9,9-dioctylfluorene-2,7-diyl)
(PFO) and poly[4-(octyloxy)-9,9-diphenylfluoren-2,7-diyl]-<i>co</i>-[5-(octyloxy)-9,9-diphenylfluoren-2,7-diyl] (PODPF) β-domains
both have shorter lifetime than those of the glassy conformation for
the longer effective conjugated length and rigid chain structures.
Besides, β-conformational regions have larger fluorescence anisotropy
for the low molecular rotational motion and high chain orientation,
while the low anisotropy in glassy conformational regions shows more
rotational freedom of the chain and efficient energy migration from
amorphous regions to β-conformation as a whole. Finally, ultrastable
ASE threshold in the PODPF β-conformational films also confirms
its potential application in organic lasers. In this regard, FLIM
and FAIM measurements provide an effective platform to explore the
fundamental photophysical process of conformational transitions in
conjugated polymer