Emission properties of MEH-PPV and its Derivatives
Date Issued
2005
Date
2005
Author(s)
Chou, Hsuan-Liang
DOI
zh-TW
Abstract
The objectives of this dissertation were to modify the poly[2-(2’-ethyl-hexyl)-oxy)-5-meth-oxy-p-phenylenevinylene] (MEH- PPV) through the heat treatment, copolymerization, blending and cross-reactions with poly(2,3-diphenyl-5-octyl-p-phenylene vinylene) (DPO-PPV) to adjust the emitting color, enhance the quantum efficiency and increase the lifetime for their prepared polymer light emitting diode (PLED).
Followings are the results being carried out in this dissertation:
1. The effects of heat treatments on the chemical structure, PL properties and EL performance of MEH-PPV were investigated. The maximum PL quantum yield after heat treatment was 6.5 times that of the untreated MEH-PPV, which was attributed to the reduction of chain aggregations and the interruption of conjugation length. The maximum EL quantum yield of their prepared ITO/PANI/MEH-PPV/Ca/AL light emitting diodes (PLED) was 46 (at 3 V) times that of the untreated sample.
2. The copolymerization of MEH-PV with DPO-PV via the Gilch route tended to form an alternative copolymer. As a result, the emission color of electroluminescence (EL) of MEH-PPV could be adjusted from orange-red to blue-green by copolymerization. However, the turn-on voltage of the prepared light emitting diode device was increased and the EL efficiency was decreased with the content of DPO-PV in copolymer.
3. The effects of bending with DPO-PPV on the optoelectronic properties of MEH-PPV were investigated. MEH-PPV and DPO-PPV are basically immiscible. The lower turn-on voltage for their prepared PLED compared to the pristine MEH-PPV was attributed to the “type II” heterojuction between the hole transport MEH-PPV segments and the electron-transport DPO-PPV segments. All the polyblends had the higher EL quantum yields than both pristine MEH-PPV and DPO-PPV. Although the EL spectrum of polyblend was blue-shifted with increasing the content of DPO-PPV, the majority of EL emission was from the MEH-PPV segments. DPO-PPV chains only played a supporting role to enhance the emission of MEH-PPV.
4. MEH-PPV/DPO-PPV immiscible blends turned to form a blend copolymer after thermal treatment that drew these two polymer segments closer in a vertically segregated structure. Because the charges were easily captured in the heterojuction zones, both the EL quantum efficiencies and stability of polyblends were greatly improved by thermal treatments.
5. The effects of manufacture parameters of PLED, such as the thicknesses of cathode Ca and conductive PEDOT layer, on the electroluminescent properties were investigated. The turn-on voltage of the prepared PLED was decreased and the EL intensity was increased by applying the PEDOT layer.
Subjects
MEH-PPV
有機發光二極體
PLED
Type
thesis