PFO/PFO:MEH-PPV 이중 발광층을 이용한 고분자유기발광다이오드의 제작과 특성 연구
Fabrication and Characterization of Polymer Light EmittingDiodes by Using PFO/PFO:MEH-PPV Double Emitting Layer
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초록
최적 소자구조에 의한 고분자 발광다이오드의 외부 양자효율 향상을 위해 스핀코팅 방법으로 ITO/PEDOT:PSS/(PFO)/PFO:MEH-PPV/LiF/Al 구조의 발광소자를 제작하고 전기, 광학적 특성을 조사 하였다. ITO(indium tin oxide) 투명전극을 양극으로 사용하고 정공수송층으로 PEDOT:PSS[poly(3,4- ethylenedioxythiophene):poly(styrene sulfolnate)]를 사용하였으며, 발광물질로는 PFO[poly(9,9-dioctylfluorene)] 와 MEH-PPV [poly(2-methoxy-5(2-ethylhexoxy)-1,4-phenylenevinyle)]를 각각 호스트와 도펀 트로 사용하였다. PFO:MEH-PPV 발광층의 두께를 약 400Å으로 형성하였고, MEH-PPV의 농도는 9 wt%로 고정하여 도핑하였다. PFO 발광층의 두께를 200~300Å의 범위로 변화시켜 전계발광 특성을 비교 해 본 결과, 두께가 약 250Å 부근에서 가장 우수한 광학적 특성이 관찰되었으며, 13V의 인가전압에서 각 각 약 400 mA/cm2의 전류밀도와 1500 cd/m2의 휘도가 관찰되었다. 또한 PFO 발광층을 2중으로 구성한 소자(PFO/PFO:MEH-PPV)가 단일 발광층을 갖는 소자 (PFO:MEH-PPV)에 비해 발광휘도 및 전류 효율 에서 약 3배의 향상된 특성을 보여주었다.
Abstract
To improve the external quantum efficiency by means of the optimization of the polymer light emitting diodes(PLEDs) structure, the PLED with ITO/PEDOT:PSS/(PFO)/PFO:MEH-PPV/LiF/Al structure were fabricated and investigated the electrical and optical properties for the prepared devices. ITO(indium tin oxide) and PEDOT:PSS [poly (3,4-ethylenedioxythiophene): poly(styrene sulfolnate)] were used as transparent anode film and hole transport materials, respectively. PFO[poly(9,9-dioctylfluorene)] and MEH-PPV[poly(2-methoxy-5(2-ethylhe xoxy)-1,4-phenylenevinyle)] were used as the light emitting host and dopant materials. The doping concentration of MEH-PPV was 9 wt% with thickness of about 400. We investigated the dependence of the PFO thickness ranging from 200 to 300 on the electrical, optical properties of PLEDs. Among prepared PLED devices with different PFO thicknesses, the highest value of the luminance was obtained for the PLED device with 250 in thickness. As a result, the current density and luminance ware found to be about 400 mA/cm2 and 1500 cd/m2 at 13V, respectively. In addition, the luminance and current efficiency of PLED device with double emitting layer (PFO/PFO:MEH-PPV) were improved about 3 times compared with the one with single emitting layer (PFO:MEH-PPV).
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