Bathocuproine (BCP) or tris(acetylacetonato)ruthenium(III) (Ru(acac)3) is used as the exciton‐blocking layer (EBL) in photovoltaic cells. The difference in thickness‐dependent efficiency ...characteristics between the blockers (see Figure) is that the Ru(acac)3 energy‐level alignment allows for the transport of holes from the cathode to the C60 acceptor level, whereas BCP relies on metal‐deposition‐induced damage for charge transport.
We relate the chemical structure of a series of methyl (Me) substituted group III metal tris(8-quinolinolato) chelates (nMeq3M: n = 0, 3, 4, 5; M = Al3+, Ga3+) to their photoluminescence (PL), ...electroluminescence, and thermal properties. Methylation of the 8-quinolinol ligand at the 3 or 4 position (pyridyl ring) results in a factor of 1.4 and 3.0 enhancement of PL quantum efficiency (φPL), respectively, whereas methylation at the 5 position (phenoxide ring) results in a factor of ∼3.0 decrease in φPL relative to the unsubstituted analogue. Electroluminescent quantum efficiencies of undoped organic light-emitting devices using the aluminum tris(8-quinolinolato) chelates are 1, 0.45, 1.4, and 0.80% for unsubstituted 5-, 4-, and 3-methyl-8-quinolinol ligands, respectively. Devices made with the latter two ligands have a higher operating voltage to generate the same current density. Similar trends were observed for methylation of gallium tris(8-quinolinolato) chelates. We relate these results to the thermal properties of the compounds measured by simultaneous differential scanning calorimetry and thermal gravimetric analysis. The C-4 methylated derivatives exhibit ∼60 °C lower crystalline melting points than all other derivatives, indicating the weakest cohesive forces between molecules. Unlike Alq3, both the C-4 and C-5 methylated derivatives show no recrystallization of the glassy state below 500 °C and exhibit ∼20−25 °C higher glass transition temperatures. We infer that methylation of the 8-quinolinol ligand reduces intermolecular interactions and consequently impedes charge transport through the film.
Cryptococcus gattii was recognized as an emerging infection in the Pacific Northwest in 2004. Out of 62 total infections in Oregon since the outbreak, 11 were in solid organ transplant (SOT) ...recipients. SOT recipients were more likely to have disseminated disease and higher mortality than normal hosts, who mostly had isolated mass lesions. The median time from transplantation to C. gattii diagnosis was 17.8 months. The primary sites of infection were lung (n = 4), central nervous system (n = 3), or both (n = 4). The Oregon‐endemic strain, VGII (subtypes IIa and IIc) was present in 10 of 11 patients; the median fluconazole minimum inhibitory concentration (MIC) was 12 μg/mL (range 2–32 μg/mL) for this strain. We found C. gattii infection among organ transplant recipients was disseminated at diagnosis, had low cerebrospinal fluid cryptococcal antigen titers, and was associated with an elevated fluconazole MIC and high attributable mortality.
Stimulated emission by optical pumping of solid-state organic materials has been well known since the late 1960s following thefirst demonstrations of laser action in dye-doped gels and molecular ...crystals. Interest in this field has been revived by the demonstration of efficient, long-lived and intense electroluminescence in both polymeric and small-molecular-weight organic thin films, which indicates the possibility of laser action in these materials. Several recent studies of optically pumped polymers have reported emission phenomena suggestive of laser action. Here we present clear evidence for laser action from optically pumped, vacuum-deposited thin films of organic molecules, in both slab-waveguide and double-heterostructure configurations. This realization of laser action in conducting organic thin films should open the way to the development of a new class of electrically pumped laser diodes.
Lasing action in organic vertical-cavity surface-emitting laser (OVCSEL) structures is demonstrated. Optically pumped OVCSELs with an active layer composed of a thin-film organic semiconductor ...tris-(8-hydroxyquinoline) aluminum (Alq$_3$) doped with DCM laser dye produced very narrow linewidth (0.2 ± 0.1 angstrom), high-power (3 watts) emission that could be varied in different devices from orange to red. The efficient energy transfer from Alq$_3$ to DCM results in a threshold input energy of 300 microjoules per square centimeter. An operational lifetime > 10$^6$ laser pulses was achieved for a device operated well above threshold in atmosphere. The linewidths above threshold are Fourier trans-form-limited and could potentially be narrowed further.
We study triplet exciton diffusion in the archetype organic material 4,4′-bis(
N-carbazolyl)biphenyl (CBP) commonly used as a conductive host in the emissive zone of organic light emitting devices. ...Using time-resolved spectral decay ensuing from the diffusion of an initially localized triplet population to a spatially separated phosphor doped region, we model the delayed fluorescence and phosphorescence decays based on non-dispersive triplet transport. Fits to the model yield a diffusion coefficient of
D
=
(1.4
±
0.3)
×
10
−8
cm
2/s, and a triplet–triplet bimolecular quenching rate constant of
K
TT
=
(1.6
±
0.4)
×
10
−14
cm
3/s. The results are extended by doping a wide energy-gap molecule into CBP that serves to frustrate triplet transport, lowering both the diffusion coefficient and annihilation rate. These results are used to model a recently demonstrated white organic light emitting device that depends on triplet diffusion in CBP to excite spatially separate fluorescent and phosphorescent doped regions of the emissive layer. We determine the extent to which diffusion contributes to light emission in this structure, and predict its performance based on ideal lumophores with unity quantum yield.
Copper phthalocyanine/C60/2,9‐ dimethyl‐4,7‐diphenyl‐1,10‐phenanthroline/Ag heterojunction organic solar cells are grown on low‐cost SnO2–F‐coated glass using organic vapor‐phase deposition (see ...figure). The bulk heterojunction (BHJ) solar cell with nanoscale CuPc protrusions shows a 2.5 % power‐conversion efficiency under 1 sun illumination. The high efficiency in BHJ solar cells is attributed to the increased exciton dissociation efficiency at the CuPc/C60 interface.
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