Polymer light-emitting diodes electron-transport layer

Huang, R Shih P.-L Shu, C.-R Chi, Y and Jen, A. K.-Y. 2009. Highly efficient white polymer light-emitting diodes based on lithium salts doped electron transporting layer. Adv. Mater. 21 361-365. 

The electroluminescent performance of single-layer polymer light-emitting diodes with their emissive layer of PVK and electron transporting molecules of iridium(III)[bis(4,6-difluorophenyl)-pyridinato-N,C ]-picolinate has been investigated [84]. 

M.-Y. Hwang, M.-Y. Hua, and S.-A. Chen, Poly(pyridine-2,5-diyl) as electron-transport/hole blocking layer in poly(phenylene vinylene) light-emitting diode, Polymer, 40 3233-3235, 1999. 

Different two layer light emitting diodes (LEDs) have been tested using the aromatic oxadiazole polymers as electron transporting layer, with PPV as emissive layer. It was found that the use of the aromatic oxadiazole polymers can realise efficient light emission using stable aluminum metal as cathode. No definite enhancement of electroluminescence efficiency has yet been observed. This can probably be explained by the fact that PPV and the oxadiazole polymers 18-20 have similar reduction potentials, and therefore by analogy similar LLMO levels. 

As discussed in Section 10.2.3, PVP and DNA have been used to wrap and water-solublize SWNTs. For specific actuator, electrical and electro-optic applications, SWNTs have been wrapped by piezoelectric polyvinylidene fluoride and trifluor-oethylene copolymer [50] or with conjugated polymers [51, 52]. The conjugated polymer used to form a composite with MWNTs and an electron-transport layer in light-emitting diodes is poly(m-phenylene-vinylene-co-2,5-dioctyloxy-p-phenylene-vinylene) (PmPV) [53]. Wrapping coupled with electron doping has been achieved with polyethylene imine to form p-n junction devices ([40], see footnote 1). 

Within the last years, oxadiazoles like 2-(biphenyl)-5-(4-tert.butylphenyl)-1,3,4-oxadiazole (PBD) 2 have been frequently applied in organic light emitting diodes [3]. Here the electron withdrawing oxadiazole unit dominates the electronic properties and the oxadiazole compounds act as electron injection and transport layers. Furthermore, 2,5-diphenyloxa-diazoles have been used as building blocks in thermostable polymers and they are highly fluorescent as well. 

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