Femtosecond Microscopy of Charge Transport in Perovskite Thin Films

非技术描述：半导体中的电荷传输是决定太阳能电池和发光二极管等器件效率的重要过程。Peroxides材料是一类新的半导体，由于其极低的成本和易于制造的丰富的起始材料，是非常有前途的硅的替代品。 在过去的5年里，钙钛矿太阳能电池的效率接近20%，超过了包括有机和非晶硅太阳能电池在内的其他技术。 一个主要的研究挑战是对电荷传输特性和膜结构之间的关系的不完全理解，这阻碍了材料设计的合理方法。这项研究解决了这一挑战，通过直接成像电荷如何在空间和时间上移动，以实现有效电荷传输的设计原则，从而揭示钙钛矿薄膜中电荷传输的限制因素。 该项目的跨学科性质为培训K-12，本科生和研究生提供了一个完美的平台，以获得纳米技术和可再生能源研究前沿的经验。 技术描述：Peroxide薄膜在下一代太阳能电池应用中极具前景。 解开与器件效率相关的控制电荷传输的机制的主要困难在于这些钙钛矿薄膜的复杂和异质形态。 电荷载流子的动力学和运输是如何影响形态的全面理解是需要的最佳设备的设计。 解决这一挑战需要实验工具，能够映射形态依赖的动态和运输直接与同时空间和时间分辨率。 在这个项目中，飞秒瞬态吸收显微镜提供了在空间和时间以及钙钛矿薄膜中的晶界上的电荷传输的首次测量。光激发后的电荷群和动力学成像同时具有~200 fs的时间分辨率和~50 nm的空间精度。 为了了解结晶度、畴大小和晶界等形态如何影响传输，将瞬态吸收显微镜与原子力显微镜和X射线散射测量相关联。 这项研究揭示了电荷传输和形态之间的关系，为高效器件提供合理的设计原则。

Non-technical description:Charge transport in semiconductors is an important process that determines efficiency for devices such as solar cells and light emitting diodes. Perovskite materials, a new class of semiconductors, are very promising alternatives to silicon because of their extreme low cost and ease of fabrication with abundant starting materials. In the past 5 years, perovskite solar cells have demonstrated efficiency approaching 20%, surpassing other technologies including organic and amorphous silicon solar cells. A major research challenge is an incomplete understanding of the relationship between charge transport properties and film structure, which prevents a rational approach in material design. This research addresses this challenge by unraveling limiting factors for charge transport in perovskite thin films by directly imaging how charges move in space and in time to enable design principles for achieving efficient charge transport. The interdisciplinary nature of the project provides a perfect platform for training K-12, undergraduate, and graduate students to gain experience at the frontiers of nanotechnology and renewable energy research. Technical description:Perovskite thin films are highly promising for next generation solar cell applications. A major difficulty in unraveling mechanisms controlling charge transport relevant for device efficiency lies in the complex and heterogeneous morphology of these perovskite thin films. A comprehensive understanding of how charge carrier dynamics and transport are affected by morphology is required for the design of optimal devices. Addressing this challenge requires experimental tools that are capable of mapping morphology-dependent dynamics and transport directly with simultaneous spatial and temporal resolutions. In this project, femtosecond transient absorption microscopy provides first-of-a-kind measurements of charge transport in space and time and across grain boundaries in perovskite thin films. Charge populations and dynamics following photoexcitation are imaged with simultaneous ~200 fs temporal resolution and ~50 nm spatial precision. To gain understanding of how morphology such as crystallinity, domain size, and grain boundary affect transport, transient absorption microscopy is correlated with atomic force microscopy and X-Ray scattering measurements. This research unravels the relationship between charge transport and morphology to provide rational design principles for efficient devices.