Triplet excitons, polymer films

Poly(541) pristine films of this polymer exhibited a photoinduced transient absorption band at around 700 nm. The transient signal decayed monoexponentially with a lifetime of 7 (is under Ar atmosphere, accelerating to 1.5 (is under O2 atmosphere. These transient bands are assigned to Ti > T transitions of polymer triplet excitons (3P ) formed in the amorphous polymer pristine films. 

The inclusion of 5 wt% PCBM [l-(3-methoxycarbonyl)propyl-l-phe-nyl-[6,6]C6i] in the spin-coating solutions resulted in efficient polymer emission quenching for all the polythiophenes studied. The transient absorption spectra of the amorphous poly(541)/PCBM blend film. At 10 ps exhibited an absorption peak around 700 nm, similar to that observed for the poly(541) pristine film. The shape of the transient spectrum varied with time, with the absorption peak shifting from 700 nm at 10 is to 900 nm for time delays >100 (is, demonstrating the formation of two distinct transient species in the blend film. The monoexponential lifetime was t = 8 (is under Ar atmosphere and significantly shortened under 02 atmosphere. Monoexponential phase is therefore assigned to the decay of poly(541) triplet excitons. 

The spin 1 /2 polaron and spin 1 triplet exciton ODMR of a wide variety of n-conjugated polymer films, solutions, blends, and LEDs was shown to yield a... 

Energy migration in polymer films via triplet or singlet excitons is potentially applicable to "photon harvesting". Unfortunately many polymers possess pendent chromophores that absorb only in the UV. Experiments at 77K on poly(2-vinylnaphthalene)... 

Both hole charges and electrons that are introduced into the polymer film combine there into excitons, as either singlet or triplet states. An exciton is a pairing, consisting of an excited electron and a hole. The electroluminescence occurs by the transition from the excited excitons into the ground state by emission of radiation. 

The improved order in films cast from toluene may also be induced by prolonged illumination at low temperatures, as recently discovered at the Technion [155]. Delocalized photoexcitations among adjacent chains may lead to several characteristic properties that are not common in isolated chains. These are [71] (i) reduced PL quantum efficiency, (ii) PL redshift, (iii) relatively large generation of PP excitations, rather than intrachain excitons, (iv) more substantial delayed PL due to PP recombination, (v) reduced formation efficiency of triplet excitons since the intersystem process is hampered by the interchain delocalization [156], and (vi) increased exciton dissociation efficiency in Ceo" doped polymer films. It is thus important to review the ultrafast excitation dynamics in MEH-PPV in comparison with those of DOO-PPV. 

Electrons and holes capture one another within the polymer film and form either singlet or triplet excitons. Of these, the singlet excitons may decay radiatively, giving out light that is observed through one of the electrodes, which must be semitransparent. The internal quantum efficiency i7i , defined as the ratio of the number of photons produced within the device to the number of electrons flowing in the external circuit, is given by... 

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