Sub-turn-on exciton quenching due to molecular orientation and polarization in organic light-emitting devices
Sub-turn-on exciton quenching due to molecular orientation and polarization in organic light-emitting devices
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DOI：
10.1126/sciadv.abb2659
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发表时间：
2020-08-01
期刊：
影响因子：
13.6
通讯作者：
Holmes, Russell J.
中科院分区：
文献类型：
--
作者：
Bangsund, John S.;Van Sambeek, Jack R.;Holmes, Russell J.
有机发光器件（OLED）的效率通常受到滚降（roll-off）的限制，其中效率随着偏压的增加而降低。在大多数OLED中，滚降主要是由于激子猝灭而发生的，激子猝灭通常被认为仅在器件开启以上才起作用。使用锁定检测的光致发光，我们发现，这一假设是不是普遍有效的，发光可以被淬灭>20%，在偏置低于turnon. We表明，这种低偏置淬灭是由于空穴积累的电子传输层（ETL）的固有极化诱导。此外，我们证明了在沉积期间选择非极性ETL或加热可使这些损失最小化，从而使效率提高> 15%。这些结果揭示了优化效率的设计规则，阐明了超稳定玻璃如何改善OLED性能，并证明了在低偏压下量化激子猝灭的重要性。
The efficiency of organic light-emitting devices (OLEDs) is often limited by roll-off, where efficiency decreases with increasing bias. In most OLEDs, roll-off primarily occurs due to exciton quenching, which is commonly assumed to be active only above device turn-on. Below turn-on, exciton and charge carrier densities are often presumed to be too small to cause quenching. Using lock-in detection of photoluminescence, we find that this assumption is not generally valid; luminescence can be quenched by >20% at biases below turn-on. We show that this low-bias quenching is due to hole accumulation induced by intrinsic polarization of the electron transport layer (ETL). Further, we demonstrate that selection of nonpolar ETLs or heating during deposition minimizes these losses, leading to efficiency enhancements of >15%. These results reveal design rules to optimize efficiency, clarify how ultrastable glasses improve OLED performance, and demonstrate the importance of quantifying exciton quenching at low bias.