基于异质外延构筑高质量PbS量子点/CH3NH3PbI3复合晶体薄膜与高效宽光谱光伏器件

The application of PbS quantum dots (QDs) offers broad interests for the design of panchromatic solar cells with wide spectral response ranging from the visible to near-infrared region of the solar spectrum. However, the use of PbS sensitizer in quantum dot solar device cause some problems of high surface defect density and short carrier diffusion length, which seriously restrict the improvement of photovoltaic performance. In consideration of material structure and attribute, we propose a design solution to construct high-quality PbS QDs/CH3NH3PbI3 perovskite heterocrystalline composite film and high-performance photovoltaic device with wide spectral response based on atomically heteroepitaxy in this project. On one hand, the excellent interfacial quality achieved as a result of heteroepitaxial growth allows the effective passivation of surface defects, and on the other hand, the utilization of remarkable long-range carrier transport characteristic of perovskites enables the significant increase of carrier diffusion length. Herein, firstly, the PbS QDs/CH3NH3PbI3 perovskite heterocrystalline composite film will be attained via modified vapor-assisted solution process. Secondly, the dependence of photoelectric properties of the films and photovoltaic performance of the corresponding devices on the structure parameters of composite films will be carefully studied. Thirdly, the mechanism of atomically heteroepitaxial growth will be explicated, the model for energy-band structure and theory for charge transfer dynamics between PbS and CH3NH3PbI3 will be established, and the mechanism of carrier behavior, such as generation, separation, transport and recombination in the target devices will be elaborated. The designed photovoltaic device is expected to comprehensively realize broadband light harvesting, efficient charge separation and fast carrier transport. Therefore, the study is of particular importance for the development of high-performance photovoltaic devices with wide spectral response.

PbS量子点在设计可见至近红外波段宽光谱太阳能电池方面应用前景广阔。然而，表面缺陷态密度高、载流子扩散长度短等问题严重制约量子点光伏器件性能。本项目从材料的晶体结构和本征属性出发，提出基于异质外延构筑高质量PbS量子点/CH3NH3PbI3复合晶体薄膜与高效宽光谱光伏器件的设计思路：1）通过外延生长获得良好的界面质量，有效钝化量子点表面缺陷态；2）结合钙钛矿优异的载流子长程输运特性，显著提高载流子扩散长度。拟利用气相辅助液相法制备PbS量子点/CH3NH3PbI3异质复合薄膜；研究薄膜光电性质和器件光伏性能对复合薄膜结构参数的依赖关系；明确原子尺度异质外延生长机制，建立PbS和CH3NH3PbI3之间的能带结构模型和电荷转移动力学理论，阐明目标器件内部载流子产生、分离、输运、复合等行为机理。以期全面实现宽光谱吸收、高效电荷分离和快速载流子输运。本研究对于发展高效宽光谱光伏器件具有重要意义。

近年来，量子点（Quantum Dots）和钙钛矿（Perovskites）作为两类极富潜力的新型半导体光伏材料，成为光伏技术研究领域的前沿热点，为开发高效率、低成本的下一代光伏器件开辟了崭新方向。窄带隙无机PbS量子点能够通过量子尺寸效应实现吸收光谱范围向近红外拓展，提高长波区域的太阳光能量收集效率；同时有望利用多重激子产生效应，实现单结太阳能电池Shockley-Queisser极限（32%）的突破。新型有机无机杂化钙钛矿材料（如CH3NH3PbI3）具备结晶度良好、缺陷态密度低、载流子扩散距离长、制备工艺简单等优点；历经10年发展，其光电转换效率从3.8%急剧攀升至25.2%。然而，当前仍存在一些关键问题制约器件光伏性能，例如量子点薄膜缺陷态密度高、载流子扩散距离短；钙钛矿材料光谱响应范围局限、电荷抽取效率有待提高等。目前，量子点和钙钛矿光伏器件性能距离其潜力目标还有较大的发展空间。如何设计构筑高质量光电薄膜，全面实现载流子的高效生成、有效分离和快速输运，对于发展下一代高效光伏器件具有重要意义。基于此，我们开展了一系列研究工作。采用新型离子交换法和一步反溶剂法制备了PbS量子点和CH3NH3PbI3钙钛矿薄膜；通过界面工程和能带工程，合理构筑兼具表面缺陷态低、电荷抽取效率高、载流子扩散距离长等优异特性的高质量光电薄膜；揭示了目标器件光伏性能对薄膜结构参数的依赖关系，并通过参数优化指导高效光伏器件的优化设计，制备获得基于PbS量子点和CH3NH3PbI3钙钛矿的太阳能电池效率分别达4.08%和18.18%；明确了光伏器件内部载流子行为机理，建立了功能层之间的能带结构模型和电荷转移动力学理论，阐明了目标器件内部载流子产生、分离、输运、复合等行为机理；探讨了量子点与钙钛矿这两类光伏材料在杂化太阳能电池中的协同增效作用，如促进钙钛矿结晶、光吸收互补、加速载流子分离、提升载流子传输、改善稳定性等。这些研究工作可为构筑高质量光电薄膜与高性能光伏器件提供很好的借鉴和参考。