Influence of Energetic Disorder on Exciton Lifetime and Photoluminescence Efficiency in Conjugated Polymers

Abstract

Using time-resolved photoluminescence (TRPL) spectroscopy the exciton lifetime in a range of conjugated polymers is investigated. For poly(p-phenylenevinylene) (PPV)-based derivatives and a polyspirobifluorene copolymer (PSBF) we find that the exciton lifetime is correlated with the energetic disorder. Better ordered polymers exhibit a single exponential PL decay with exciton lifetimes of a few hundred picoseconds, whereas polymers with a larger degree of disorder show multiexponential PL decays with exciton lifetimes in the nanosecond regime. These observations are consistent with diffusion-limited exciton quenching at nonradiative recombination centers. The measured PL decay time reflects the time that excitons need to diffuse toward these quenching sites. Conjugated polymers with large energetic disorder and thus longer exciton lifetime also exhibit a higher photoluminescence quantum yield due to the slower exciton diffusion toward nonradiative quenching sites.

Highly Luminescent Encapsulated Narrow Bandgap Polymers Based on Diketopyrrolopyrrole

“…We note that these findings are in direct contradiction to the recent study which suggests that polymers with higher energetic disorder should have higher emissive quantum yields. 20 We suggest that the introduction of the encapsulating macrocycle prevents the formation of non-radiative quenching sites. The emissive quantum yields clearly demonstrate our encapsulation strategy has been highly effective, resulting in the first examples of highly fluorescent DPP polymers in the solid state potentially allowing for their use in sensors, LEDs and visible light communications (VLC) applications.…”

Measuring Energetic Disorder in Organic Semiconductors Using the Photogenerated Charge-Separation Efficiency

“…Various transport models include energetic disorder as a fitting parameter 3,[10][11][12][23][24][25][26][27][28][29][30] . Most commonly, carrier mobility is measured as a function of temperature and fitted to a theoretical model of thermally activated hopping.…”

“…6. MEH-PPV, σ was estimated to be 105 meV via Monte Carlo charge transport simulations of exciton lifetimes29 . From time-of-flight measurements, the disorder in MEH-PPV was found to be 63 meV or 92 meV (depending on the solvent)46 .…”

Green and stable processing of organic light-emitting diodes from aqueous nanodispersions

“…Besides, the efficiency of the presented devices is comparatively low, as exciton quenching in ladder polymers is substantial due to the high carrier mobility. 15 Here, we provide the first detailed study on the fabrication, optimization and characterization of PLEDs, prepared from aqueous nano-dispersions of the poly(p-phenylenevinylene) (PPV)-based polymer emitter poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV), blended with polystyrene (PS) to aid film formation. Although the efficiency of our devices seems to be the highest reported so far for organic light-emitting diodes with an active layer processed from a nanodispersion, our main aim is to demonstrate the compatibility between aqueous nanoparticle dispersion technology and the fabrication of stably operating PLEDs.…”