Efficient Solution-Processed Nanoplatelet-Based Light-Emitting Diodes with High Operational Stability in Air
Efficient Solution-Processed Nanoplatelet-Based Light-Emitting Diodes with High Operational Stability in Air
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DOI：
10.1021/acs.nanolett.8b00456
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发表时间：
2018-06-01
期刊：
影响因子：
10.8
通讯作者：
Brovelli, Sergio
中科院分区：
文献类型：
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作者：
Giovanella, Umberto;Pasini, Mariacecilia;Brovelli, Sergio
胶体纳米片（NPLs）由于其高效和窄带发光，被认为是具有高色纯度的溶液可加工发光二极管（LED）的有希望的候选者。然而，到目前为止，NPL-LED的记录效率明显低于基于球形纳米晶体的更多研究的设备。这对于发红光的NPL-LED尤其如此，其最佳报道的外部量子效率（EQE）限于0.63%（对于绿色NPL-LED，EQE = 5%）。在这里，我们通过引入极性和聚电解质聚合物的电荷调节层来解决这个问题，所述聚合物专门设计有互补的三甲基铵和膦酸酯官能团，所述官能团在正交极性介质中相对于NPL活性层提供高溶解度，与金属阴极的相容性，以及通过在偏压下形成极化界面来控制电子注入的能力。通过这种协同方法，我们在完全溶液处理的LED中在658 nm处实现EQE = 5.73%（色饱和度98%）。值得注意的是，暴露在空气中将EQE增加到8.39%，超过红色NPL-LED的最佳报告超过1个数量级，并为任何颜色嵌入溶液沉积的有机夹层的量子点LED创造了新的全球记录。考虑到NPL的发射量子产率（40 +/-5%），该值对应于接近1的内部量子效率。值得注意的是，我们的器件在没有封装的情况下在空气中连续驱动超过5小时，表现出出色的操作稳定性，从而证实了NPL在高效、高稳定性、饱和LED方面的潜力。
Colloidal nanoplatelets (NPLs), owing to their efficient and narrow-band luminescence, are considered as promising candidates for solution-processable light-emitting diodes (LEDs) with ultrahigh color purity. To date, however, the record efficiencies of NPL-LEDs are significantly lower than those of more-investigated devices based on spherical nanocrystals. This is particularly true for red-emitting NPL-LEDs, the best-reported external quantum efficiency (EQE) of which is limited to 0.63% (EQE = 5% for green NPL-LEDs). Here, we address this issue by introducing a charge-regulating layer of a polar and polyelectrolytic polymer specifically engineered with complementary trimethylammonium and phosphonate functionalities that provide high solubility in orthogonal polar media with respect to the NPL active layer, compatibility with the metal cathode, and the ability to control electron injection through the formation of a polarized interface under bias. Through this synergic approach, we achieve EQE = 5.73% at 658 nm (color saturation 98%) in completely solution processed LEDs. Remarkably, exposure to air increases the EQE to 8.39%, exceeding the best reports of red NPL-LEDs by over 1 order of magnitude and setting a new global record for quantum-dot LEDs of any color embedding solution-deposited organic interlayers. Considering the emission quantum yield of the NPLs (40 +/- 5%), this value corresponds to a near-unity internal quantum efficiency. Notably, our devices show exceptional operational stability for over 5 h of continuous drive in air with no encapsulation, thus confirming the potential of NPLs for efficient, high-stability, saturated LEDs.