金属卤化物钙钛矿材料中光生载流子动力学研究

Solution-processed CH3NH3PbX3 (where X=Cl, Br, I) with their outstanding optoelectronic properties of large absorption coefficient, low trap density, and long balanced charge diffusion lengths, have recently demonstrated great potential for both light harvesting and light emission applications. Record photovoltaic efficiencies exceeding 20% have been achieved with the CH3NH3PbX3/TiO2 heterojunction type devices. Low threshold amplified spontaneous emission (ASE) and high Q lasing have been demonstrated with lead halide perovskite thin films and micro/nano-structures, respectively. Despite these achievements, the mechanisms for ultrafast high efficiency photo-induced exciton dissociation and long-range balanced charge carrier diffusion in these perovskites still remain poorly understood. Concerns with the toxicity of the Pb necessitate the development of lead free perovskite. In order to reveal these mechanisms and problems for further advances in light harvesting of these perovskites, we propose to do a systematic charge carrier dynamics investigation on them with spatial-resolved ultrafast spectroscopy and micro-/nano-meter range morphology and composition analysis techniques. The morphology and composition dependent individual charge carrier dynamical processes (exciton generation; dissociation and recombination; charge carrier diffusion, transporting and extraction; etc.) will be monitored in functional devices. The exciton dissociation and charge carrier diffusion processes are crucial for perovskite sensitized solar cells. They are also crucial for perovskites based light emission and lasing devices. Therefore, this research project will also contribute to the understanding and optimization of perovskite based light emission applications.

研究发现，低温溶液法制备的铅卤化物钙钛矿材料，由于其强的可见光吸收、低缺陷态浓度和长程平衡的载流子扩散传输等特点，在太阳电池和发光方面的应用存在非常大的潜能。基于钙钛矿/二氧化钛异质结的太阳能电池中，器件的光电转化效率目前已超过20%。钙钛矿薄膜的受激发射和钙钛矿微纳单晶的高品质激光发射也相继被报道。然而，钙钛矿材料的一些关键性的机理问题仍然没有得到明确的解释，如高效快速光生激子解离及其随后长程平衡传输的深层次物理机理、无铅化所引起的载流子动力学变化等。深刻的探测及理解钙钛矿光电器件中的光生载流子动力学过程，对提升光电器件效率提升及其无铅化的应用，具有极其重要的物理指导意义。本课题将关联研究钙钛矿材料的微纳结构、微区超快光谱及器件的光电性能，直接观测微纳形貌与成份的不均匀性对光生载流子动力学及器件性能的影响，从而揭示出其高效转化机理及制约因素，最终优化设计出更高性能的光电子器件。

本项目旨在探究及阐明钙钛矿光电器件中的载流子动力学过程，同时关联研究钙钛矿材料的微纳结构、微区超快光谱及器件的光电性能，并通过直接观测微纳形貌与成份的不均匀性对光生载流子动力学及器件性能的影响，从而揭示出其高效光电转化机理及制约因素，最终优化设计出更高性能的光电子器件。因此本项目的研究成果，对提升器件效率及稳定性应用，具有极其重要的物理指导意义。我们主要的研究结果包括：1） 通过大分子掺杂三维钙钛矿，以及添加大分子构建了多维混杂钙钛矿，实现了微纳尺度下载流子传输与提取效率的调控，从而获得高效稳定的钙钛矿电池器件；2） 研究了钙钛矿界面的载流子传输动力学，例如探究不同晶面的二氧化钛/钙钛矿、铜铟镓硒（CIGS）/钙钛矿和二硫化钼/钙钛矿异质结中电荷/能量传输过程，这些研究成果有助于优化基于钙钛矿光电子器件效率。3） 探索了钙钛矿的不同结构维度、形貌维度中载流子行为的差异，以及对相对应的发光性质的影响，该系列研究成果为实现高效低成本的新型钙钛矿发光器件奠定了理论基础。基于本项目的支持，已培养博士研究生两名，硕士研究生6名，发表高质量SCI论文20篇，一作或通讯的18篇。基于本项目支持，也积极参加国内外合作交流，促进了该领域的发展。