Zeng Yicheng, Liu Xiaonan, Liu Yuan, Chen Weiwei, Liu Fangze, Li Hongbo
Experimental Center of Advanced Materials, School of Materials Science and Engineering, Beijing Institute of Technology, Beijing, 100081, China.
State Key Laboratory of Molecular Reaction Dynamics and Dynamics Research Center for Energy and Environmental Materials, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, Liaoning, 116023, China.
Adv Mater. 2024 May;36(19):e2310705. doi: 10.1002/adma.202310705. Epub 2024 Mar 1.
The external quantum efficiency (EQE) in light-emitting diodes (LEDs) based on isotropic quantum dots has approached the theoretical limit of close to 20%. Anisotropic nanorods can break this limit by taking advantage of their directional emission. However, the progress towards higher EQE by using CdSe/CdS nanorods (NRs) faces several challenges, primarily involving the low quantum yield and unbalanced charge injection in devices. Herein, the seeded growth method is modified and anisotropic nanorods are obtained with photoluminescence quantum yield up to 98% by coating a gradient alloyed CdZnSe shell around conventional spherical CdSe seeds. This intermediate alloyed CdZnSe shell combined with a subsequent rod-shaped CdZnS/ZnS shell can effectively suppress the electron delocalization in the typical CdSe/CdS nanorods due to their small conduction bandgap offset. Additionally, this alloyed shell can reduce the hole-injection barrier and create a larger barrier for electron injection, both effects promoting a balanced injection of electrons and holes in LEDs. Hence, LEDs are reached with high brightness (160341 cd m) and high efficiency (EQE = 22%, current efficiency = 23.19 cd A), which are the highest values to date for nanorod LEDs.
基于各向同性量子点的发光二极管（LED）的外量子效率（EQE）已接近20%的理论极限。各向异性纳米棒可以利用其定向发射打破这一极限。然而，使用CdSe/CdS纳米棒（NRs）提高EQE的进展面临若干挑战，主要涉及器件中的低量子产率和电荷注入不平衡。在此，通过在传统球形CdSe种子周围包覆梯度合金化CdZnSe壳层，对种子生长法进行了改进，获得了光致发光量子产率高达98%的各向异性纳米棒。这种中间合金化CdZnSe壳层与随后的棒状CdZnS/ZnS壳层相结合，可以有效抑制典型CdSe/CdS纳米棒中的电子离域，因为它们的导带隙偏移较小。此外，这种合金化壳层可以降低空穴注入势垒，并为电子注入创造更大的势垒，这两种效应都有助于在LED中实现电子和空穴的平衡注入。因此，获得了具有高亮度（160341 cd m）和高效率（EQE = 22%，电流效率 = 23.19 cd A）的LED，这是迄今为止纳米棒LED的最高值。
