Center for Opto-Electronic Materials and Devices, Korea Institute of Science and Technology (KIST), Seoul, 02792, Republic of Korea. Department of Materials Science and Engineering, Yonsei University, Seoul 03722, Republic of Korea.
Nanotechnology. 2019 Jan 18;30(3):035207. doi: 10.1088/1361-6528/aaed98.
ZnO nanoparticles (NPs) of 4-5 nm, widely adopted as an electron transport layer (ETL) in quantum dot light emitting diodes (QD-LEDs), were synthesized using the solution-precipitation process. It is notable that synthesized ZnO NPs are highly degenerate intrinsic semiconductors and their donor concentration can be increased up to N = 6.9 × 10 cm by annealing at 140 °C in air. An optical bandgap increase of as large as 0.16-0.33 eV by degeneracy is explained well by the Burstein-Moss shift. In order to investigate the influence of intrinsic defects of ZnO NP ETLs on the performance of QD-LED devices without a combined annealing temperature between ZnO NP ETLs and the emissive QD layer, pre-annealed ZnO NPs at 60 °C, 90 °C, 140 °C, and 180 °C were spin-coated on the annealed QD layer without further post-annealing. As the annealing temperature increases from 60 °C to 180 °C, the defect density related to oxygen vacancy (V ) in ZnO NPs is reduced from 34.4% to 17.8%, whereas the defect density of interstitial Zn (Zn) is increased. Increased Zn reduces the width (W) of the depletion region from 0.21 to 0.12 nm and lowers the Schottky barrier (Ф) between ZnO NPs and the Al electrode from 1.19 to 0.98 eV. We reveal for the first time that carrier conduction between ZnO NP ETLs and the Al electrode is largely affected by the concentration of Zn above the conduction band minimum, and effectively described by space charge limited current and trap charge limited current models.
4-5nm 的氧化锌纳米粒子（NPs）被广泛用作量子点发光二极管（QD-LED）中的电子传输层（ETL），采用溶液沉淀法合成。值得注意的是，合成的 ZnO NPs 是高度简并的本征半导体，其施主浓度可以通过在空气中 140°C 退火提高到 N=6.9×10 cm。由简并引起的光学带隙增加高达 0.16-0.33eV，可以很好地用 Burstein-Moss 位移来解释。为了研究 ZnO NP ETL 中的本征缺陷对 QD-LED 器件性能的影响，而无需 ZnO NP ETL 和发射 QD 层之间的组合退火温度，在退火的 QD 层上旋涂预退火的 ZnO NPs，温度分别为 60°C、90°C、140°C 和 180°C，而无需进一步后退火。随着退火温度从 60°C 升高到 180°C，ZnO NPs 中与氧空位（V ）相关的缺陷密度从 34.4%降低到 17.8%，而间隙 Zn（Zn）的缺陷密度增加。增加的 Zn 减小了耗尽区的宽度（W）从 0.21 至 0.12nm，并将 ZnO NPs 和 Al 电极之间的肖特基势垒（Ф）从 1.19 降低至 0.98eV。我们首次揭示，载流子在 ZnO NP ETL 和 Al 电极之间的传导主要受到导带底以上 Zn 浓度的影响，并通过空间电荷限制电流和陷阱电荷限制电流模型有效地进行描述。
