钙钛矿/铁电异质结太阳能电池的光伏效应及电荷传输机制研究

Organic-inorganic hybrid perovskite materials are a promsing, low cost,easily synthesized set of materials.They act as light absorber and both electron and hole transport. High efficiency exceeding 15% for the perovskite based solar cells has been reached and thus they have attracted much attention recently. However, the photophysical properties made them so promsing are still unclear, e.g. what is the precise role of each interface in the device? what is the dissociation mechanism of carrier in the perovskite? BiFeO3 (BFO) with perovskite structure has high ferroelectric polarization and good electron transport properties. Ferroelectrics have been used to improve the photovoltaic or photoelectrochemical properties in oxide semiconductor and organic photovoltaic solar cells because the ferroelectric polarization is able to modulate the energy band or accelerate the dissociation of carrier(exciton).Therefore,the introduction of BFO to perovskite should be beneficial to enhance the photovoltaic effect of perovskite based solar cells and be a good candidate for investigating the role of different interfaces and the dissociation mechanism of carrier(exciton)in the perovskite. In this project,CH3NH3PbI3 thin films will be prepared by ultrasonic spray pyrolysis method. Planar heterojunctions perovskite solar cells by using BFO nanoparticle layer as electronic transport layer and bulk heterojuntion perovskite solar cells based on the co-deposition of a combined BFO-perovskite layer will be formed. The relationship between micro/nano structure and photovoltaic effect will be analyzed. The ferroelectric polarization on photovoltaic effect, charge transport characteristics, and fluorescence quenching properties will be investigated. Our work will help us to clarify the precise role of each interface in the device and the dissociation mechanism of carrier(exciton) in the perovskite. This project therefore will provide insight into ways finding a new photovoltaic technology with good photovoltaic effect.

有机-无机杂化钙钛矿太阳能电池由于其低的制作成本及优越的光伏效应而备受瞩目，但目前关于钙钛矿电池中各个界面对电荷分离及传输的作用机制尚不清楚。铁酸铋光伏材料不仅具有良好的电子传导特性，而且可以通过铁电极化调制优化异质结界面处的能级排列来促进电荷的分离。因此将铁酸铋引入到钙钛矿太阳能电池中不仅可望提高其光电转换效率，也是我们研究钙钛矿电池中电荷分离与传输机制的理想对象。本次申请通过超声喷雾热解法制备CH3NH3PbI3薄膜，研究BFO/CH3NH3PbI3平面异质结和它们的共混膜体异质结的微/纳结构特征对光伏特性的影响，研究脉冲极化电压对异质结电池的光伏效应及载流子的传导特性、荧光淬灭特性和复合特性的影响，分别揭示肖特基势垒和异质结界面处势垒对电荷分离及传输的作用机制，揭示铁电退极化场与载流子复合之间的内在关系，为制作具有更加优越光伏特性的有机-无机杂化钙钛矿太阳能电池提供实验和理论依据。

有机铅卤钙钛矿光吸收材料以其可调的窄带隙、高的光吸收系数、低的光生激子结合能、高的载流子迁移率以及长的平衡载流子扩散距离等优点，在世界范围内掀起钙钛矿太阳能电池研究热潮。作为钙钛矿太阳能电池中的光吸收材料，钙钛矿薄膜不仅要吸收太阳光，还要完成光生载流子的分离和传输。因此，制备高质量的钙钛矿薄膜对提高太阳能电池器件性能尤为重要。本研究从钙钛矿薄膜生长、形貌调控角度出发，深入探讨了钙钛矿薄膜制备中的工艺条件和PbI2前驱体微结构和结晶，以及高载流子迁移率的BaSnO3新型电子传输材料对钙钛矿薄膜质量以及光伏性能的影响。最终，通过薄膜形貌和质量的调控以及电子传输层的优化实现太阳能电池光电转换效率（PCE）提升，为以后高性能太阳能电池器件制备和机理研究提供基础。本项目重要研究结果包括：.（1）采用极性溶剂DMF“活化” 致密的PbI2前驱体，实现了高质量MAPbI3薄膜的可控制备。通过极性溶剂DMF的协助，致密的PbI2前驱体可快速转化为高表面覆盖、高光吸收、无PbI2残留的钙钛矿薄膜，提出了极性溶剂DMF协助制备MAPbI3薄膜的溶解-再结晶作用机理。.（2）率先将铁电聚合物P(VDF-TrFE)添加剂用作两步连续旋涂法PbI2前驱体的结晶钝化剂和形貌调控剂，成功地实现了对PbI2前驱体结晶和表面形貌的调控，达到了高质量MAPbI3薄膜可控制备的目的。发现少量聚合物添加制备的MAPbI3薄膜具有高结晶度，大晶粒尺寸、互联晶体结构和长的载流子寿命，组装的电池器件最优PCE达到13.24%，稳态功率输出达12.83%。.（3）使用未退火的湿PbI2前驱体实现了简单快速可控制备平整、高结晶度、无PbI2残留的高质量MAPbI3薄膜。提出了MAI分子原位取代湿PbI2前驱体中DMF溶剂分子组装成MAPbI3的作用机理，湿PbI2前驱体制备的最优器件PCE可达到15.49%。.（4）成功采用高载流子迁移率、分散性良好的高结晶BSO纳米颗粒单独作为电子传输材料制备了平面结构PSCs。发现FTO衬底的高BSO纳米颗粒覆盖和合适的BSO层厚度是制备高性能BSO基平面PSCs的关键，实验中制备的最优BSO基器件的PCE为10.96%，而传统TiO2纳米颗粒基器件PCE为9.36%。