钙钛矿金属有机卤化物太阳能电池材料的力电光多场耦合效应及其对光伏转换性能的影响

Organometal trihalide perovskite solar cells could have significant improvement on the energy structure and environmental problems for China as well as the entire planet due to their low cost, low-power consumption, flexibility and high efficiency. However, because of the complexity of the multi-physical coupling, its microscopic mechanism, inner interaction and the resulted macroscopic phenomena in perovskite materials are still not well-investigated, and thus its effects on the photovoltaic performance of perovskite solar cells should be further elucidated. Motivated by these observations, we seek to explain the mechanical-electro-optical coupling in perovskite materials and to reveal the effects of ferroelectric polarization, piezoelectricity, ion migration and electrochemical strain on photovoltaic performance. This study will include, 1) developing a scale-span AFM experimental mechanics method to realize a real-time in-situ mechanical-electro-optical coupling observation; 2) revealing the microscopic properties and mechanism of local mechanical-electro-optical coupling based on micro-nano scale; 3) clarifying the effects of this multi-physical coupling on photovoltaic conversion performance on the perspective of the solar cell devices. This project will give a deeper understanding on mechanical-electro-optical coupling in perovskite materials and make it possible to provide a powerful experimental mechanics tool. It also provides a pathway to improve the photovoltaic conversion efficiency of the perovskite solar cells via controlled multi-physical couplings.

新型钙钛矿有机金属卤化物太阳能电池具有成本低、能耗小、柔韧可塑和转换效率高等诸多优点，对改善我国乃至世界能源结构和环境问题具有非常重要意义。然而钙钛矿太阳能电池材料表现出复杂的多场耦合效应，其微观机制、相互作用以及宏观表象当前并不清楚，对钙钛矿太阳能电池光伏转换性能的影响也有待揭示。本项目旨在阐明钙钛矿有机金属卤化物材料的力电光多场耦合效应，并揭示铁电极化、压电效应、离子运动和电化学应变对材料光伏转换的影响。研究内容包括（1）发展基于AFM的跨尺度实验力学方法，实现钙钛矿太阳能材料力电光多场耦合效应实时原位观测；（2）在微纳尺度揭示钙钛矿材料局域力电光多场耦合效应微观性质及机理；（3）在器件层面阐明多场耦合效应对太阳能电池光伏转换性能的影响。项目将加深我们对钙钛矿太阳能电池多场耦合效应的理解，为这类材料提供强有力的实验力学工具，并为通过多场耦合调控提升钙钛矿太阳能电池光伏转换效率提供方向。

该项目从优化材料和器件工艺，铁电极化和离子迁移等多场耦合效应，以及对光电转换性能机理开展研究。详细研究成果如下：.优化钙钛矿材料和器件制备工艺。（1）通过锡金属部分置换铅离子制备锡铅钙钛矿太阳能电池，光电转换效率达到12.46%。（2）云母基底柔性钙钛矿太阳能电池最佳光电转换效率为18.0％，电池连续弯曲5000次，保持初始效率的91.7％，表现优异的机械性能；（3）锂镍基钙钛矿太阳能电池，获得了20.44%的最佳光电转换效率。.原位原子力显微技术研究钙钛矿铁电极性。（1）MAPbI3单晶中，极性与非极性畴共存。极性畴和非极性畴都随相变产生明显的记忆效应，畴结构在相变温度以上消失，相变温度下恢复。极性畴区域光电流减弱，极性抑制光电流的产生。（2）MAPbI3存在的交替极性和非极性畴结构，极性畴为非中心对称晶体结构，表现出铁电性；非极性畴区为中心对称晶体结构，表现出反铁电性；铁电-反铁电畴壁提供了光生电子传输的通道，调控了铁电相和反铁电相之间的翻转。.通过透射电子显微技术研究钙钛矿中离子迁移。在极低的电子束剂量下（0.7 e Å-2）成功地采集了MAPbI3的钙钛矿型原子结构，揭示了钙钛矿分解普适路径以及阳离子有序的中间相结构；低温并没有阻碍钙钛矿的分解，反而会导致快速的非晶化转变；碳包覆可以起到稳定结构抑制分解的作用，减弱离子迁移。.钙钛矿多场耦合效应扩展应用。常规服役压力载荷下，钙钛矿晶胞各向异性占主导；超过可以承受临界压力，即超高压载荷下，结晶相转变为非晶相，带隙减小，呈现金属化性质；临界服役压力载荷下，出现微观结构和能级结构行为突变。采用钙钛矿材料CsFAMA作为光敏介质构建光伏传感器，发现光照和电场都能够诱导器件内部发生离子迁移并改变其能带结构和输运特性，其目标识别准确率提高263%。