全无机钙钛矿光增益的缺陷效应研究

Thanks to the superior optoelectronic properties and emission color tunability across the full visible range, the all-inorganic halide perovskites are highly promising for solar cells, LEDs and laser applications. However, the surface defect induced optical loss turns out to be serious in the all-inorganic perovskite crystals, which plagues the optical gain performance and limits the potential as laser gain media. In this proposal, we intend to reveal the main loss mechanism related to the surface defects in inorganic perovskites by both experimental and theoretical investigations, find effective approaches to suppressing the optical loss, and, eventually, realize the enhancement of optical gain and reduction of laser threshold by nearly two orders of magnitude. The detailed research contents include: first, we will study the surface defect induced nonradiative recombination mechanisms in inorganic perovskite crystals by exploiting the surface composition analysis, thermally stimulated current spectra, photoluminecence spectra, and first-principle calculations on defect formation energy and defect energy levels. Then, we will explore the surface defect passivation methods including chemical modifications by halide-salt solution and organic molecules, laser annealing and atomic layer deposition. Finally, we will investigate the effects of the various surface passivation methods on the optical gain performance and laser threshold, and establish the optimized surface-treatment approach for optical gain enhancement. This project will shed light on the surface defect physics of inorganic perovskites and advance the development of inorganic perovskite-based lasers.

全无机卤素钙钛矿因其优异的光电性质和可见光全谱发光可调性，在太阳能电池、LED、激光、单光子源等光电器件领域具有广阔的应用前景。这一新型半导体在激光方面的主要瓶颈是：表面缺陷损耗严重，导致光增益性能不佳，限制了其激光发展。本项目针对这一关键科学问题，拟结合实验和理论研究，揭示无机钙钛矿中主要表面缺陷损耗机制，探索有效的表面缺陷钝化方式，实现单光子激发下低阈值光增益和激光阈值近两个数量级的降低。具体研究内容包括：利用表面成份分析、热激电流谱和荧光光谱等手段，并结合第一性原理对缺陷能级等进行理论计算，揭示无机钙钛矿晶体中引起非辐射复合的主要表面缺陷来源，探索表面化学修饰、激光退火和原子层沉积等处理方式对表面缺陷的钝化情况，研究不同表面钝化方式对光增益和激光阈值的影响，确立光增益增强的最佳表面处理方案。本项目的开展将有望阐明无机钙钛矿表面缺陷物理，推进无机钙钛矿在激光应用领域的发展。

本项目以推进无机钙钛矿单晶在激光领域应用为目标牵引，针对单晶表面光学损耗严重影响光增益这一关键问题，分析无机钙钛矿中导致非辐射损耗的主要缺陷机制，探索有效的表面缺陷钝化方式，优化光增益，降低激光阈值。本项目执行期间完成了计划研究的内容，主要研究了无机钙钛矿表面非辐射损耗的主要缺陷机制、无机钙钛矿单晶表面处理和缺陷钝化机制以及不同表面钝化方式对光增益和激光阈值的影响。在钙钛矿单晶制备方法、激光机制、以及激光器件制备等方面取得了一定的进展：（1）揭示了钙钛矿单晶表面卤素空位对发光性能的影响，阐明了钙钛矿单晶中独特的离子迁移效应可以有效钝化卤素空位缺陷态，进而提出了原位电场调控荧光发射，这对理解钙钛矿单晶发光机制和激光性能提升提供了重要参考。（2）发展了一种基于与铅原子结合并牢固锚定在钙钛矿纳米单晶表面的配体策略，在高温下仍保持良好钝化作用，为发展基于钙钛矿纳米晶的相干激光光源和光子发射器件提供了新的方案。（3）开发了一种全新的液相结晶方法，该方法可以原位钝化钙钛矿表面的卤素空位缺陷态，并实现了卤化物钙钛矿微晶的大批量可控制备，进而获得了超高光增益系数和超低阈值的激光出射，极大促进了集成光子和微/纳光电器件的发展。在本项目的支持下，研究成果以通讯作者发表了Nano Letters, ACS Photonics以及Advanced Optical Materials等高水平期刊论文17篇，申请发明专利1项。培养了四名硕士生和一名博士生。