聚合物发光二极管中的负电容效应

Negative capacitance in polymer light-emitting diodes

采用交流阻抗谱技术,研究了以共轭聚合物(poly[2-methoxy,5-(2′-ethylhexoxy)-1,4-phenylenevinylene])(MEH-PPV)为发光层,以带有胺基的聚芴共聚物poly[(9,9-bis(3′-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)](PF-NR2)为电子传输层的发光二极管的交流响应特性.对于结构为ITO/PEDOT/MEH-PPV/PF-NR2/Al的发光器件,交流阻抗谱中出现了负电容效应(negative capacitance),根据对其Cole-Cole图的分析,MEH-PPV/PF-NR2界面的交流响应可用一个RLL并联电路来模拟,实验结果表明,PF-NR2层既是电子传输层同时又充当了空穴阻挡层的作用,并给出了解释这种以PF-NR2/Al为阴极的器件效率提高的微观机理.

A.c. electrical properties of the heterostructured polymer light-emitting diode consisting of poly[ 2-methoxy-5-（2＇-ethyl- hexyloxy）- 1, 4-phenylenevinylene ] （ MEH- PPV） as the light-emitting layer, and poly [ （ 9,9 - bis （ 3＇- （ N, N- dimethylamino） propyl）-2, 7- fluorene ）-alt-2, 7-（ 9, 9-dioctylfluorene ） ] （ PF-NR2 ） as the electron-injecting layer, are studied by using impedance spectroscopy. Negative capacitance in impedance spectroscopic data has been observed. According to the Cole-Cole plot of the device ITO/PEDOT/MEH-PPV/PF-NR2/A1, the a.c. response of MEH-PPV/PF-NR2 interface can be explained in terms of the equivalent circuit model of a parallel combination of an inductance L and a resistance RL . The experiments showed that PF-NR2 could act as an electron injecting and hole blocking layer. We propose an energy band structure schematic diagram to explain the enhancement of the EL efficiency in the ITO/PEDOT/MEH-PPV/PF-NR2/Al structure.