Charge injection and photooxidation of single conjugated polymer molecules
Charge injection and photooxidation of single conjugated polymer molecules
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DOI：
10.1021/ja031929x
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发表时间：
2004-04-07
影响因子：
15
通讯作者：
Barbara, PF
中科院分区：
文献类型：
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作者：
Park, SJ;Gesquiere, AJ;Barbara, PF
有机电子器件(如有机发光二极管、太阳能电池等)中电荷转移和氧化损伤的复杂、耦合机制。通过单分子光谱学与金属电极电荷注入相结合的新技术阐明了这一点。实验采用了夹心式器件结构(Au/TPD/MEH-PPV：PMMA/SiO_2/ITO)，本质上是一种带有电荷阻挡层(SiO_2)的改性OLED，以抑制ITO电极上的电荷注入。观察到嵌入器件中的MEH-PPV共轭聚合物分子的荧光(光致发光)表现出不同的时间和电偏压效应。其中包括： (I)由于MEH-PPV与TPD空穴传输层中的空穴之间的相互作用而导致的荧光猝灭；(Ii)由于光氧化产生的MEH-PPV上的化学缺陷而导致的荧光猝灭，或称为“光漂白”；以及(Iii)一种新的工艺，即通过外部注入载体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所认为的完全不同，而且还表明有机材料中的光漂白、电荷传输和持续光导之间存在着密切的关系。
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.