高性能、低成本新型量子点发光二极管的研究

Based on our newly invented quantum-dot LED (QLED)—insertion of insulator thin-layer QLED (patent was filed in March 2014), this proposal intends to study the related fundamental sciences. The work shall focus on the key aspects of this new type of QLED devices. We aim to study working mechanisms of the new type of QLEDs—especially the function(s) of the insulator thin-layer, extension of high efficiency and high power devices to all colors from the demonstrated red prototype QLEDs, white QLEDs for both display and solid-state-lighting applications, high-performance QLEDs based on non-cadmium quantum dots, and failure mechanisms of QLEDs at work conditions. To our knowledge, our prototype red QLEDs represent the best-performing solution-processed red LEDs to date and comparable to the state-of-art vacuum-deposited OLEDs. Specifically, our QLED exhibits color-saturated deep-red emission, high external quantum efficiency (EQE) up to 20.5%, low efficiency roll-off (> 15% of EQE at 100 mA cm-2), and a long operational lifetime of more than 100,000 hours at 100 cd m-2. More importantly, similar to polymer LEDs (PLEDs), this new type of QLEDs, except the top silver electrodes, were fabricated by solution-processable techniques. In comparison to the best PLEDs reported in literature, this new type of QLEDs were comparable in terms of the maximum EQE (20.5%). Its performance becomes even more advantageous while comparing to PLEDs at a high power density needed for practical applications. Fundamental studies related to this new type of QLEDs should offer China a good position to commercialize QLEDs, which is of importance for both display and solid-state-lighting.

2013年下半年，我们发明了一种性能优越的新型量子点发光二极管（QLED）：绝缘插层QLED。以红光原型器件为例，包括效率（20.5%的外量子效率）、大功率性能（100 mA cm-2的条件下，外量子效率>15%）和器件寿命（100 cd m 2的初始亮度下半衰期超过100,000小时）在内的综合性能优于目前所有溶液工艺制备的LED。更加重要的是，这种新型QLED的制备工艺与聚合物LED（PLED）类似，以低成本的溶液加工为基础。与目前最好的PLED比较，其最大EQE并不逊色，且其大功率性能超过所有PLED。本项目计划研究这种新型QLED相关基础科学问题，包括其工作机制——尤其是绝缘层的作用、多色大功率高效器件、分别适用于固态照明和显示的白光QLED、高性能非镉量子点器件、QLED的失效机制等。深入研究这种拥有完全知识产权的新型QLED，将使我国在QLED基础研究与产业化方面占据制高点。

QLED结合高效稳定无机晶体发光中心和溶液加工的优势，有望实现效率高、稳定性好、大功率性能优异、低成本的大面积器件。同时，量子点材料发光波长连续可调、发光光谱半峰宽窄、色纯度高，在高色域的显示屏和高显色指数的白光光源调制方面具有独特的优势。本项目聚焦于QLED走向应用所必须克服的关键基础科学问题，在以下四个方面取得了创新成果：.A、量子点材料的激发态合成控制：提出“量子点激发态合成控制”的研究思路，为QLED设计并合成了“量身定制”的量子点。通过合成化学、配体化学与现代谱学相结合，实现了CdSe-CdS核壳结构等量子点模型系统的激发态控制，获得了~100%辐射复合效率、单通道复合的非闪烁量子点。提出“熵配体”的概念，大幅（~2-6个数量级）提升量子点的溶解度，为电致发光量子点的合成和设计奠定基础。.B、QLED的工作机理：实现单量子点电致发光器件，一方面制备了迄今为止单光子纯度最高的室温电泵单光子源器件，展现了溶液量子点应用于单光子源器件的广阔前景；另一方面发展了研究量子点电致发光的理想模型系统，为后续设计高效QLED提供指导。.C、具有实用价值的高性能QLED原型器件：在理解限制QLED效率关键因素的基础上大幅简化器件结构，设计新的电子传输层，在去除超薄绝缘层的前提下仍然制备了高性能红光和绿光器件，解决QLED从实验室走向产业化的一个痛点问题。.D、无镉无铅QLED：通过重新设计InP核壳量子点结构与合成路线，将不含铅、镉量子点LED的效率大幅提高，达到与CdSe基量子点LED相似水平。