Optically detected magnetic resonance (ODMR) studies of pi-conjugated polymer films and light-emitting diodes (LEDs)

Joseph Shinar; Neil C. Greenham; Richard H. Friend

doi:10.1117/12.219558

15 September 1995 Optically detected magnetic resonance (ODMR) studies of π-conjugated polymer films and light-emitting diodes (LEDs)

Joseph Shinar, Neil C. Greenham, Richard H. Friend

Author Affiliations +

Proceedings Volume 2528, Optical and Photonic Applications of Electroactive and Conducting Polymers; (1995) https://doi.org/10.1117/12.219558
Event: SPIE's 1995 International Symposium on Optical Science, Engineering, and Instrumentation, 1995, San Diego, CA, United States

Abstract

The photoluminescence (PL)-, electroluminescence (EL)- and conductivity ((sigma) )-detected magnetic resonance of poly(p-phenylene vinylene) (PPV), poly(p-phenylene ethynylene) (PPE), and PPV/CN-PPV LEDs is reviewed and discussed. In the PPV- and PPE-based LEDs the polaron resonance is EL-quenching, but in the PPV/CN-PPV bilayer diodes it contains both EL-quenching and enhancing components. While the (sigma) -detecting polaron resonance is invariably quenching in the PPV devices, in some of the PPE-based LEDs it is (sigma) -enhancing. The PL-enhancing resonance is attributed to nonradiative recombination of trapped polaron pairs, which reduces their population and consequently the rate at which they nonradiatively quench singlet excitons; the EL-enhancing resonance is tentatively assigned to the same mechanism in the CN-PPV layer, but other mechanisms are not ruled out. Interchain coupling, some defects induced by structural disorder, and sites adjacent to dopant molecules (e.g., C₆₀) apparently enhance the generation of these trapped polarons as well as intersystem crossing from the singlet to the triplet manifold. The EL- and (sigma) - quenching resonances are attributed to the fusion of like-charged free polarons to bipolarons, which is also suspected to be induced by disorder and/or impurities. The LEDs also exhibit half-field EL- and (sigma) -detected triplet exciton resonances. Triplet-triplet fusion to singlets and the role of triplets as quenching sites for singlet excitons are discussed as possible mechanisms leading to the triplet resonances.

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Joseph Shinar, Neil C. Greenham, and Richard H. Friend "Optically detected magnetic resonance (ODMR) studies of π-conjugated polymer films and light-emitting diodes (LEDs)", Proc. SPIE 2528, Optical and Photonic Applications of Electroactive and Conducting Polymers, (15 September 1995); https://doi.org/10.1117/12.219558

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