钙钛矿太阳能电池理论研究：界面结构、性质与调控

For the interfaces in peroviskite solar cell, theoretical investigation is behind the experimental research and development on them. We will establish relatively sophisticated interfacial micro-models for peroviskite solar cell and reveal the micro-mechanism of photoelectric properties affected by the interfaces (structures and properties). We will use the first principles calculation aided by device simulation to systematically study the local lattice structures and photoelectronic properties of the interfaces located in electron transfer material | CH3NH3PbI3 light-absorbing layer | hole transfer material | metal electrode at electronic, atomistic and device levels. For the local lattice structures, lattice direction match, lattice mismatch, chemical composition in the adjacent layers, bond lengths, bond angles and lattice defects will be considered. For the photoelectric properties, complex dielectric function, absorption coefficient, energy band alignment, interface states and their densities, work function and potential barriers will be calculated. The effects of energy band alignment, height of potential barrier and quantity of density of states are focused for the cell’s performance (open-circuit voltage, short-circuit current, fill factor and photoelectric conversion efficiency). Then more potential manipulation measures for the interfaces will be proposed basing on the previous experimental manipulation methods. The aim of this research is to construct the interface models, to deeply understand the relationship among the local lattice structures of the interfaces, interface properties and perovskite solar cell’s performances. As theoretical guides, quantitative results at multi-scale will be helpful to design chemical components of the cell’s materials and those at the interfaces, to modify the interface structures, to manipulate the interface properties, to take the advantage of so called interface engineering and then to improve the cell’s performances.

钙钛矿太阳能电池界面理论研究滞后于实验研发。拟为该电池建立相对完备的界面微观模型并探讨界面结构和性质对电池性能的影响机理：采用第一性原理计算辅以器件模拟方法在电子、原子和器件三种结构层次上系统研究电子传输层|CH3NH3PbI3光吸收层|空穴传输层|金属电极各界面的局域晶格结构（晶向匹配、晶格失配、紧邻层成分、键长、键角及晶格缺陷等）和光电性质（复介电常数、吸收系数、能带匹配、界面态及其密度、功函数和势垒等）。重点探究界面能带匹配、势垒和态密度对电池性能（开路电压、短路电流、填充因子和光电转换效率）的影响规律，在已有实验界面调控方法基础上寻求更多可能的界面调控措施。目的是用多层次结构的定量数据建立该电池的界面模型，深刻理解界面局域结构-性质-电池性能的相关关系，为设计电池（界面）化学成分、修饰界面结构、调控界面性质、发挥所谓“界面工程”的作用提供参考，为提高电池性能提供理论引导和帮助。

按项目原定计划，完成了有机-无机杂化钙钛矿（MAPbI3）典型界面电学性能的研究，纯无机钙钛矿（CsPbI3）界面电学性能研究和钙钛矿太阳能电池器件模拟工作，重要结论摘要如下：1）通过对SnO2（110）/MAPbI3（100），MAPbI3（100）|NiO（110）MAPbI3|Au和MAPbI3|WZ-ZnO界面的晶格结构和光电性质研究，除了MAPbI3|Au界面处没有出现新的界面态外，其他界面处费米能级附近都出现了界面态，界面态的主要来源于I原子的5p轨道，O原子的2p轨道，Pb的6s和6p轨道； 2）通过对PCBM吸附MAPbI3表面和苯乙铵（PEA+）钝化MAPbI3（110）表面稳定性及其光电性质研究，发现PCBM的吸附增强了MAPbI3的光吸收系数，而PEA+作为钝化剂可以有效地减弱MAPbI3（110）表面上的电子态，MAPbI3（110）表面在费米能级处的峰值减小了约一半且带隙值明显减小；3）通过对MAPb1-xAgxI3的光电性质研究，发现当掺杂浓度达到5%时，很容易发现价带向高能级移动，费米能量进入价带，这表明 MAPb0.95Ag0.05I3具有p型导电行为；4）SnO2（110）/ CsPbI3（100）和SnO2（110）/ CsPbI2Br（100）界面的晶格结构和光电性质研究，发现界面在费米能级处存在由I-5p轨道和O-2p轨道组成的界面态；5）通过对 Mn掺杂CsPbI2Br晶体结构和光电性质研究，发现Mn取代掺杂CsPbI2Br时，Mn-3d轨道强烈局域在费米能级处而形成中间带，这意味着Mn取代掺杂CsPbI2Br将形成中间带半导体、拓宽光子吸收范围、提升光子吸收利用率；6）研究缺陷态对钙钛矿太阳能电池性能的影响，发现缺陷态密度对钙钛矿太阳电池性能的危害始终存在，缺陷态密度对钙钛矿太阳电池光电性能临界值为10^16 cm^-3。大于该值时，缺陷态密度对光电性能影响较大，小于该值时，缺陷态密度对光电性能影响不大。