铁电体/有机-无机杂化钙钛矿界面的载流子传输及多场耦合研究

Organic-inorganic halide perovskites have attracted much interests and been extensively studied due to its good absorption in the visible-light region, higher carrier separation, and excellent photovoltaic properties. To the best of our knowledge, BiFeO3(BFO) is the only multiferroic material at room temperature and an ideal candidate for magnetoelectric data storage. The ferroelectric domain walls in BFO are able to separate the large carriers from perovskite side and create an open-circuit voltage larger than the band gap. Moreover, the large amount of carriers from perovskite side can transport to BFO side and make it a candidate used in optically controlled devices. Based on the time dependent density functional theory as well as teraherz technique, we systematically investigate the photovoltaic effect and carrier transport in perovskite-based heterostructrues associated with the ferroelectric domain walls, interfacial structures, lattice, and doping level. We also investigate the I-V hyteresis effect caused by the reordering of the ferroelectric polarization and charge, as a consequence of the mobility and rotation of the ions. Our goal is to improve further the photovoltaic properties in perovskite-based solar cells and provide an understanding of the microscopic mechanism involved. In addition, we also focus on the interactions between photons, spins, charge, and lattice in ferroelectrics/perovskites heterostructures, in terms of its application in next-generation optoelectronic devices.

由于有机-无机杂化钙钛矿太阳能电池良好的可见光吸收、高载流子分离率及其优异的光伏性能具有广阔的应用前景，BiFeO3(BFO)的室温多铁性使其成为磁电存储器件的首选材料。本研究有机的将二者结合在一起，铁电体的铁电畴可以分离钙钛矿体系的光生载流子并进一步提升开路电压；同时钙钛矿体系提供BFO光生载流子使其有望成为光写入器件材料。采用含时密度泛函理论对激发态下铁电体/有机-无机杂化钙钛矿异质结构的铁电、界面、格点和掺杂调控光伏性能和光生载流子传输机理进行系统深入的研究，采用太赫兹等技术为异质体系的载流子传输提供实验证据；探究导致I-V曲线滞后(I-V hysteresis)的物理机制，为进一步提高钙钛矿太阳能电池光伏性能提供理论指导；研究外部光激励作用下的光子、自旋、电荷和晶格多物理场耦合机理，为设计新一代光电子器件提供材料和物理基础。

表界面问题历来是光伏材料器件领域的基础问题和难点问题，对材料器件性能的提升至关重要，针对光伏领域的这一基础科学问题，对钙钛矿异质结构的界面构型、载流子动力学、能级位置、隧穿效应和铁电效应进行了第一性原理理论计算结合实验研究。在国际上率先提出了界面电子态的概念并定义了界面电子态，发现了界面电子态可以作为除了结构之外的第二个描述界面效应的维度量，揭示了界面电子态和结构之间的耦合及相互影响机理。进一步提出了界面电子态诱导的界面的载流子隧穿和界面能隙的减少，对于界面工程优化提升光伏器件的性能具有重要意义。提出了铁电体可用于太阳能电池的电子传输层，揭示了铁电体的载流子能级、输运调控、畴壁导电的微观物理机理，并率先制备了目前效率最高的铁电体基钙钛矿太阳能电池，器件的光电性能可以被铁电极化方向所调控，拓展了铁电体在光伏器件的应用领域。对于太阳能电池中的界面电子传输的动力学驱动进行了研究，部分解决了界面能级差异所导致的热力学标准不足以解释界面电子传输的难题，对于光电器件界面电子行为的研究和界面工程提升光电器件的性能具有重要意义。实现了机器学习大数据预测新型光伏材料→DFT验证→光伏材料器件制备→产业化的全链条理性设计指导材料器件制备科学方案，首次预测了4种性能优异的无机光伏材料，为探索制备新一代高稳定性无机太阳能电池提供了优质的备选材料。