Electroluminescence of pure poly(N-vinylcarbazole) and its blends with a multiblock copolymer

Abstract

Electroluminescence (EL) in pure poly(N-vinylcarbazole) (PVK) has been observed in a simple single active layer EL device with the structure of ITO/PVK/Al (or Ca). The emitted light is violet with a maximum intensity at 426 nm; a part of the spectrum lies within the UV region. Blends of PVK with a conjugated-nonconjugated multiblock copolymer (CNMBC) previously described are also electroluminescent. In these blends a new emission peak in the EL spectra appeared and can be attributed to the emission from an exciplex formed by the two polymers. As the composition of the aforementioned blend changes from a PVK-poor to a PVK-rich ratio, the emitted light changes from green to blue. Further, blends containing 97 wt. % PVK and 3 wt. % CNMBC yielded an EL spectrum with a single emission peak different in location from either that of pure PVK or the pure CNMBC; the latter is blue with a maximum intensity at 476 nm. The EL output of the blends can be clearly seen in a brightly lit room at ambient temperature. An electron transport layer consisting of butyl-2-(4-biphenyl)-5-(4-tert-butylphenyl-1,3,4-oxadiazole) (PBD) in PMMA on the cathodic side of the EL device greatly increased the brightness of the emitted light to 200 cd/m2 in the case of a PVK-rich blend, but it had less effect on a PVK-poor blend or in pure PVK and had little effect on the pure form of the CNMBC.

The nature of trapping sites and recombination centres in PVK and PVK–PBD electroluminescent matrices seen by spectrally resolved thermoluminescence

“…In all the cases, a broad and unstructured emission band extending from 350 nm to over 650 nm, with a dominant broad maximum at 420-445 nm, was observed [6][7][8][9]. The emission at ca 420-430 nm comes from the low energy singlet excimer (full overlap carbazole units).…”

“…This emission bands about 590 nm and above 600 nm were attributed to several different mechanisms, such as aggregation, [7,9] electroplex [3,9] or phosphorescence [13,14]. In contrast to PVK, for which photophysical properties were extensively studied since many years, the PVK-PBD system was investigated much less intensively.…”

Investigation of photoexcitations of conjugated polymer/fullerene composites embedded in conventional polymers

“…Alternation in the vibronic fine structure is well known for blends of conjugated polymers and conventional polymers. [24][25][26] The luminescence maxima of the low C 60 component at 2.18 eV is blueshifted by 0.12 eV compared to the pure PS/MEH-PPV component.…”

Controlling the optical properties of a conjugated co-polymer through variation of backbone isomerism and the introduction of carbon nanotubes

“…Various polymer-processing approaches have also been reported such as the utilisation of polymer blends [12]. This method involves using a non-conjugated, noninteracting polymer as a spacer to isolate individual molecules or strands.…”