Three kinds of multi-layer light emitting diodes (LEDs) were fabricated

in which poly (phenylene vinylene) derivatives

such as poly (2-methoxy-5-(2-ethyl-hexoxy)-l

4-phenylene-vinylene (MEH-PPV)

the alternating copolymer of triphenylamine and phenylene vinylene (TPA-PPV) and the alternating copolymer triphenylamine and phenylene vinylene (TPA-DMPPV) were used as light emitting materials

Alq

3

was used as electron-transport materials

while emeraldine base form of polyaniline (PANI-EB) was used as hole-transport materials.It was found that the PANI-EB layer as a hole-transport layer introduced into the PPV derivative/Alq

3

diodes reduced the threshold voltage and enhanced the emission intensity of the diodes.This might result from decreasing of the barriers of ITO/PPV derivative interface and benefit for the hole injection and electron/hole transport.Moreover

enhancement of the diode properties resulted in PANI-EB layer is related to the structure of PPV derivatives

and an order of TPA-PPV

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MEH-PPV

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TPA-DMPPV in lightness was observed.