高性能柔性钙钛矿LED的电荷注入及发光特性研究

Perovskite light emitting diodes (Pe-LEDs) has a wide application prospect for next-generation high-definition displayer and healthy lighting systems, owing to their outstanding advantage, such as low-cost, simple process and high color quality. Particularly, flexible Pe-LEDs are gaining increasing attentions with the merit of lightweight, bendable, and portable features. It has become a frontier research subject with the rapid improvement in its electro-optical conversion efficiency in very recent years. But the technology is still in the very early stages of development, many key challenges remained for device flexibility. Currently inorganic crystalline semiconductor materials (TiO2, ZnO, etc) are mostly employed in Pe-LEDs as charge injection layer, but which has impeded the developments of flexible Pe-LEDs due to the high fabrication temperature of such materials. Therefore, the development of low temperature (<100oC) oxide film as charge transport layer is the key to realize high performance flexible Pe-LED. In our recent studies, flexible Pe-LEDs were initially achieved based on low temperature sol-gel processed amorphous oxides (SnOx) as electron injection layer. Based on this foundation, in this project, we put forward the study of high performance flexible green Pe-LEDs, where the mixed perovskite layer [APbX3 (A = CH3NH3+、NH(CH3)2+、Cs+ or their mixture，X = I-、Br-、Cl- or their mixture)] was designed as light emitting layer, low temperature sol-gel processed amorphous oxides (SnOx and NbOx) as electron injection layer and inorganic p-type oxide (CuO2，NiOx) as hole injection layer. The project focuses on the balance design of flexible green Pe-LED with matched energy level alignment, the controllable growth and the physical mechanism of high efficient electro-optical conversion. The optimizations of each function layer and interface structures will be thoroughly investigated based on the semiconductor interface engineering and energy band theory, to facilitate the injection and confinement of carrier in the perovskite active layer, and then enhance the luminescent efficiency of flexible green Pe-LEDs. The evolution law and mechanism of the internal interface within Pe-led during electroluminence operation will be systematically studied, and the interface will be optimized accordingly to improve the long-term operation stability of flexible Pe-LEDs. This proposal will break through the existing technical limitations, and provide theoretical foundation and technical support on the study of high-efficiency and stable flexible Pe-LEDs.

钙钛矿型发光二极管（Pe-LED）具有广阔应用前景，柔性Pe-LED因具有质量轻、可弯曲、便携等优点而备受关注。目前Pe-LED的电荷注入层普遍依靠晶态材料，其较高生长温度严重制约了柔性Pe-LED的发展。发展低温(<100度)电荷注入层是实现高性能柔性Pe-LED的关键。本项目提出以混合钙钛矿薄膜为发光有源层，以溶胶-凝胶法低温生长的非晶氧化物作为电荷注入层，构建高性能柔性Pe-LED。电子注入层采用n-型NbOx和SnOx，空穴注入层采用p-型CuOx和NiOx。拟重点研究柔性Pe-LED的电荷注入平衡设计、可控生长及实现高效电-光转换的物理机制。调控各功能层材料及器件界面特性，促进载流子注入和辐射复合，提高器件电光转换效率。研究工作电场下Pe-LED内部由于离子迁移导致的界面退化机制，从而优化界面结构并提高器件稳定性。为柔性Pe-LED的研制提供理论依据和技术支持。

金属卤化物钙钛矿材料受到了学术界和产业界的极大关注。目前钙钛矿太阳电池（PSCs）已成为高效太阳能电池的领跑者和最受期待的下一代光伏技术，此外，钙钛矿发光二极管（Pe-LEDs）具有颜色可调、转换效率高和成本低等优势，有望为显示和固态照明应用利用提供变革型技术支撑。本项目在刚性和柔性钙钛矿材料生长和光电器件领域开展了系统性研究，特别是针对电子传输层低温制备、原位结晶调控、缺陷精准协同钝化、抑制离子迁移和抗弯折可靠性等共性科学难题，提出了一系列原创性解决方案，取得了一系列具有国际影响的原创性研究成果。代表性研究结果及科学意义如下：（1）设计并实现了多种结构不同发光颜色的Pe-LEDs，并通过多种策略（包括钙钛矿材料生长、组成优化、结晶形貌控制、2D/3D维度调控）有效提高了Pe-LEDs器件的电注入发光外量子效率（EQE）和工作稳定性。（2）从器件结构入手，创新性设计并制备出新型叠合结构碳基PSCs（简称SC-PSCs），通过将电荷纵向提取和横向传输解耦，并结合单原子材料解决了相邻功能层之间的能级失配问题，大幅降低电荷转移动力学能量损失。创造了C-PSCs效率国际记录（21.6%）。另外，SC-PSCs还具有制备工艺简单、可反复拆装、方便维护、可大面积制备等突出优势。（3）提出引入微量三价阳离子(Nd3+）间隙位掺杂有效抑制了钙钛矿材料在光照和电场下的离子迁移，且不引起晶格畸变和晶体的长程有序性，显著提高了PSCs器件的工作效率和长期稳定性。（4）缺陷钝化是实现高效稳定PSCs的有效手段，但是钝化剂的选取要非常繁琐的试错过程，提出了表面钝化剂的选取原则，模拟和实验结果都证明当聚合物含有酯基C=O双键时对钙钛矿表面缺陷的钝化效果最好。相关成果相继在国际顶刊发表并得到同行高度认可，项目资助发表期刊论文44篇，主要包括：Nature Energy, Nature Materials, Joule（2篇）, Energy&Environmental Science（3篇）, ACS Energy Letters（3篇）, Nature Communications, Advanced Functional Materials（4篇）等。此外，参与本项目研究生荣获辽宁省优秀博士论文、辽宁省优秀硕士论文等二十余项奖励。项目执行期内荣获辽宁省科技进步二等奖一项。