Direct Optoelectronic Imaging of Nanostructured Halide Perovskites

非技术描述：本项目旨在研究一种有前途的光伏材料卤化物钙钛矿中的电荷传输机制。卤化物钙钛矿化合物，包括甲基铵卤化铅，最近显示出巨大的潜力，太阳能转换效率超过20%。然而，缺乏对材料物理的基本理解。该项目旨在提取基础科学，并提供关于电荷传输机制的关键见解，以及识别更稳定的钙钛矿化合物以实现具有成本效益的光化学的指导方针。特别是，首席研究员使用了一种新的实验技术，通过扫描聚焦激光束来绘制光生电流分布。这种直接成像技术可以提取光如何转化为电荷以及电荷如何在这些材料中传输的关键信息。对高转换效率起源的基本理解不仅对基础科学很有吸引力，而且对于开发具有降低毒性和提高稳定性的更好的钙钛矿材料也至关重要。这项研究可能会导致地球丰富的材料，有望为光化学开辟一个新的范例。本项目主要针对发展迅速的纳米和能源科学领域的本科生和研究生进行教育和培训，并为K-12学生提供外展活动。技术描述：本项目研究了单晶卤化物钙钛矿纳米结构中的电荷输运，并区分了铁电性、离子迁移和电荷陷阱中占主导地位的电荷输运机制。尽管在这些材料中展示了有效的功率转换能力，但材料物理学，例如长载流子寿命和滞后光电流的起源还不清楚。由单晶卤化物钙钛矿组成的纳米线和纳米片可以消除晶界的卷积，并允许更好地理解本征性质。由单个纳米结构组成的器件通过波长依赖的扫描光电流显微镜进行研究，以确定少数载流子扩散长度如何取决于表面效应和载流子浓度。这些纳米结构在不同温度下的外电场下的直接光电成像为区分不同的电荷传输机制提供了关键的见解。压电效应的单晶纳米结构下的外部应变进行了研究。采用一种新的液体门控方法研究了氢、锂等离子在卤化物钙钛矿中的输运。该研究加深了对高转换效率起源的基本理解，并为选择更好的分子或原子来取代卤化物钙钛矿中的阳离子或阴离子制定了指导方针。

Nontechnical Description: This project aims to investigate the charge transport mechanisms in a promising photovoltaic material, halide perovskites. Halide perovskite compounds, including methylammonium lead halide, have recently demonstrated great potentials for solar energy conversion, with a power conversion efficiency above 20%. However, the fundamental understanding of the material physics is lacking. The project aims to extract fundamental science and provides key insights on the charge transport mechanisms and guidelines for identifying more stable perovskite compounds for cost-effective photovoltaics. In particular, the principal investigator uses a novel experimental technique, which maps the photogenerated current distribution by scanning a focused laser beam. This direct imaging technique allows extraction of key information on how light is converted into charge and how charge transports in these materials. The fundamental understanding of the origins of the high conversion efficiency is not only intriguing to fundamental science, but is also critical to developing better perovskite materials with reduced toxicity and increased stability. The study may lead to earth abundant materials that promise to open a new paradigm for photovoltaics. This project educates and trains undergraduate and graduate students in the rapidly advancing nanoscale and energy sciences, and offers outreach activities targeting K-12 students, underrepresented minorities.Technical Description: The project investigates the charge transport in single-crystal halide perovskite nanostructures and distinguishes the dominant charge transport mechanism among ferroelectricity, ion migration, and charge traps. Despite the demonstration of efficient power conversion capability in these materials, material physics such as the origins of long carrier lifetime and hysteretic photocurrent is not understood. Nanowires and nanoplates composed of single-crystal halide perovskites can remove the convolution of grain boundaries and allow better understanding of the intrinsic properties. Devices consisting of individual nanostructures are investigated by wavelength-dependent scanning photocurrent microscopy to determine how minority carrier diffusion lengths depend on surface effects and carrier concentration. Direct optoelectronic imaging of these nanostructures under external electric field at various temperatures provides key insights for distinguishing among different charge transport mechanisms. Piezoelectric effects are studied in single-crystal nanostructures under an external strain. The transport of different ions such as hydrogen and lithium in halide perovskites is investigated by using a novel liquid gating method. The research deepens the fundamental understanding of the origins of the high conversion efficiency and allows formulating guidelines for choosing better molecules or atoms to substitute the cations or anions in halide perovskites.