Investigating Free Charge‐Carrier Recombination in Organic LEDs Using Open‐Circuit Conditions
Investigating Free Charge‐Carrier Recombination in Organic LEDs Using Open‐Circuit Conditions
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DOI：
10.1002/adom.201801426
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发表时间：
2019-01
影响因子：
9
通讯作者：
Jinhan Wu;A. Fischer;S. Reineke
中科院分区：
文献类型：
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作者：
Jinhan Wu;A. Fischer;S. Reineke
尽管有机发光二极管（LED）广泛应用于商业应用，但仍然缺乏对发生的复合途径的全面了解。特别是需要了解带隙来确定电荷载流子采取的路径，这是进一步了解和优化最新一代薄膜 LED 技术的关键。在这里，通过测量紫外线照射下的开路电压，将最先进的有机 LED 视为太阳能电池。照明强度和温度的变化可以获得有效带隙、理想因子和复合强度。采用差分评估方法，得出这些参数的完整温度和强度依赖性。识别辐射和非辐射复合过程并用于重建外部量子效率的电流密度依赖性。所有复合事件都与有效带隙有关，该有效带隙表明发光层的客体和主体材料之间发生自由电荷复合。因此，这种方法将有助于识别和消除基于其他类型分子发射器和材料（例如钙钛矿或量子点）的 LED 中的非辐射复合损失。了解有效带隙对于实现具有最低驱动电压的 LED 也至关重要。
Although organic light‐emitting diodes (LEDs) are widely used in commercial applications, a comprehensive knowledge about the occurring recombination pathways is still absent. Especially access to the bandgap is needed to figure out which path the charge carriers take, key to further understand and optimize the latest generations of thin film LED technology. Here, state‐of‐the‐art organic LEDs are treated like solar cells by measuring the open‐circuit voltage under UV illumination. A variation of the illumination intensity and temperature gives access to the effective bandgap, the ideality factor and the recombination strength. A differential evaluation approach is implemented, yielding the full temperature and intensity dependence of these parameters. A radiative and a non‐radiative recombination process are identified and used to reconstruct the current density dependence of the external quantum efficiency. All recombination events are related to an effective bandgap that suggests free charge recombination between the guest and the host material of the emission layer. This approach will thus help to identify and eliminate non‐radiative recombination losses in LEDs based on other type of molecules emitters and materials, such as perovskites or quantum dots, as well. Knowing the effective bandgap will also be essential to realize LEDs with the lowest possible driving voltages.