Combined Macroscopic and Nanoscopic Studies of the Photovoltaic Behavior of Organic Perovskite Materials

非技术描述：开发具有成本效益的光伏电池是清洁能源、空气污染和能源安全的长期清洁能源解决方案之一。理想的策略是通过使用低成本、低温工艺沉积天然丰富的活性层来实现高效的光伏电池。有机钙钛矿是新兴的光伏材料，其特征在于其优异的结晶性，大的光学消光系数，和合适的带隙。在过去的几年中，有机钙钛矿基光伏器件的效率比任何其他太阳能电池技术都有更快的提高。然而，对有机钙钛矿的光伏行为的机制的基本理解仍处于起步阶段。该项目探索基本机制，最终目标是加工具有上级物理化学性能的有机钙钛矿材料用于太阳能电池应用，从而为可再生能源的技术发展做出贡献。教育活动与研究很好地结合在一起，包括：（1）为研究生和本科生促进纳米科学和清洁能源技术的研究培训和教学;（2）通过向公众开放的活动，如“科学家星期日”和“纳米夏令营”，让K-12学生和内布拉斯加州居民参与。该项目的目标是在宏观和纳米层面上研究与有机铅三卤化物钙钛矿材料光伏行为的物理机制相关的两个最重要的基本方面：（1）氯（Cl）浓度通过增加载流子扩散长度在增强光伏行为中的作用，以及（2）可切换光伏效应的起源。该项目建立在主要研究者在稳定的高质量晶体钙钛矿薄膜和高效钙钛矿太阳能电池器件，通过Cl掺入控制优先晶粒取向以及可切换光伏效应方面的专业知识基础上。扫描探针显微镜（包括导电原子力显微镜，压电响应力显微镜和开尔文探针力显微镜）和宏观测试技术（如瞬态光电压，瞬态光电流，阻抗谱，稳态光电流和暗电流测量）用于研究晶粒尺寸和取向对钙钛矿薄膜和器件中电荷产生，传输和复合的影响。对钙钛矿太阳能电池的纳米级研究的组合提供了对于理解光伏效应的基本物理机制和基于钙钛矿的太阳能电池器件的功能增强至关重要的信息。

Non-technical Description: Development of cost-effective photovoltaic cells is one of the long-term, clean energy solutions for clean energy, air pollution, and energy security. An ideal strategy is to achieve efficient photovoltaic cells via depositing a naturally abundant active layer using a low-cost, low-temperature process. Organic perovskites are emerging as photovoltaic materials characterized by their excellent crystallinity, large optical extinction coefficient, and a suitable bandgap. In the last several years, the organic perovskite-based photovoltaic devices have experienced a faster increase in efficiency than any other solar cell technology. However, the basic understanding on the mechanisms of the photovoltaic behavior of organic perovskites is still in its infancy. This project explores the fundamental mechanisms with the ultimate goal to process organic perovskite materials with superior physicochemical properties for solar cell applications, and thus contributes to the technological development of renewable energy sources. The educational activities are well integrated with the research including: (1) promoting research training and teaching in nanoscience and clean energy technology for graduates and undergraduate students; (2) involving K-12 student and Nebraska residents through open-to-the-public events, such as 'Sunday with a Scientist' and 'Nanocamp'.Technical Description: The goal of this project is to investigate, at both the macro- and nanoscopic levels, two of the most important fundamental aspects related to the physical mechanisms of photovoltaic behavior of the organolead trihalide perovskite materials: (1) the role of chlorine (Cl) concentration in enhancing the photovoltaic behavior through the increased carrier diffusion length, and (2) the origin of the switchable photovoltaic effect. This project builds upon the principal investigator's expertise on stable high-quality crystalline perovskite films and high-efficiency perovskite solar cell devices, control of preferential grain orientation by Cl incorporation, and the switchable photovoltaic effect. Scanning probe microscopy (including conducting atomic force microscopy, piezoresponse force microscopy and Kelvin probe force microscopy) and macroscopic testing techniques (such as transient photovoltage, transient photocurrent, impedance spectroscopy, steady photocurrent and dark-current measurements) are used to investigate the effect of grain size and orientation on charge generation, transport, and recombination in perovskite thin films and devices. A combination of nanoscale studies of perovskite solar cells provides information critically important for understanding the underlying physical mechanism of the photovoltaic effect and enhancement of the functionalities of the perovskite-based solar cell devices.