Park So-Jung, Gesquiere Andre J, Yu Ji, Barbara Paul F
Department of Chemistry and Biochemistry and the Center for Nano- and Molecular Science and Technology, University of Texas, Austin, Texas, USA.
J Am Chem Soc. 2004 Apr 7;126(13):4116-7. doi: 10.1021/ja031929x.
The complex, coupled mechanisms of charge transfer and oxidative damage in organic electronic devices (such as organic light-emitting diodes (OLED), solar cells, etc.) have been elucidated by a new technique that combines single-molecule spectroscopy with charge injection from a metal electrode. The experiments employed a sandwich device architecture (Au/TPD/MEH-PPV:PMMA/SiO2/ITO), essentially a modified OLED with a charge-blocking layer (SiO2) to suppress charge injection at the ITO electrode. The fluorescence (photoluminescence) of isolated MEH-PPV conjugated polymer molecules imbedded in the device was observed to exhibit diverse time- and electrical bias-dependent effects. These include: (i) fluorescence quenching due to interactions between MEH-PPV and holes in the TPD hole-transport layer; (ii) fluorescence quenching, or "photobleaching", due to chemical defects at MEH-PPV generated by photooxidation; and (iii) a novel process, reductive "repair" of the oxidative chemical defects by externally injected carriers. These results demonstrate a very different mechanism for photobleaching of organic conjugated materials than is generally assumed to operate and, furthermore, suggest an intimate relationship among photobleaching, charge transport, and persistent photoconductivity in organic materials.
一种将单分子光谱与金属电极电荷注入相结合的新技术，阐明了有机电子器件（如有机发光二极管（OLED）、太阳能电池等）中电荷转移和氧化损伤的复杂耦合机制。实验采用了三明治器件结构（金/TPD/MEH-PPV:PMMA/SiO₂/ITO），本质上是一种带有电荷阻挡层（SiO₂）的改良OLED，用于抑制ITO电极处的电荷注入。观察到嵌入器件中的孤立MEH-PPV共轭聚合物分子的荧光（光致发光）表现出多种与时间和电偏压相关的效应。这些效应包括：（i）由于MEH-PPV与TPD空穴传输层中的空穴相互作用导致的荧光猝灭；（ii）由于光氧化在MEH-PPV上产生的化学缺陷导致的荧光猝灭或“光漂白”；以及（iii）一种新过程，即通过外部注入的载流子对氧化化学缺陷进行还原“修复”。这些结果表明，有机共轭材料的光漂白机制与通常认为的机制非常不同，此外，还表明了光漂白、电荷传输和有机材料中持久光电导之间的密切关系。
