EAGER: Vertical-carrier-transport two-dimensional photo-harvesting devices with nanocavity enhancement

【摘要】非技术：光电探测器和光电器件是光能转化为电能的关键部件。为了评估这些器件的性能，功率转换效率是最重要的参数之一，它描述了有多少光能被转换为电能。由于近年来二维材料的进步，人们相信革命性的超薄光电器件是可能的。然而，由于这些原子薄层内的光吸收较弱，基于二维材料的光电探测器和光伏器件的功率转换效率较低。因此，有必要设计和开发新的策略来提高这些二维能量收集装置的功率转换效率。该项目将结合电气（即垂直载流子传输）和光学（即纳米腔）架构来克服这一巨大挑战。(1)由于电子和空穴的输运距离仅为几纳米，因此载流子输运效率优于体材料。(2)由于强光干涉共振，纳米腔结构显著增强了二维层内的光吸收。因此，可以大幅提高功率转换效率。这个EAGER项目将进行基础和实验相结合的研究，以验证这一科学假设，这将为开发实际高效的二维光采集设备铺平道路。技术：在大多数薄膜能量收集/转换应用中，在光吸收和半导体材料厚度之间存在长期存在的权衡。在最近出现的基于二维材料的光电探测器和光伏器件中尤其如此。由于原子层薄，它们的光-物质相互作用（例如，光吸收和能量转换效率）很弱。因此，吸收增强策略将为这些基于二维的光收集设备带来革命性的进步。另一方面，人们普遍认为最小化活性材料的体积可以抑制光电探测器在限制扩散工作模式下的噪声和热过剩载流子。它还可以最大限度地减少光电器件中载流子的重组。然而，这种优势仅适用于载流子沿垂直方向流动且以面外量子隧道为主的垂直器件架构。在本项目中，我们将开发一种基于平面纳米腔中强干涉效应的增强二维材料光-物质相互作用的基本策略，并克服能量收集装置的光吸收和膜厚度之间的限制。这一原理是相当普遍的，将应用于探索各种吸收二维材料的光谱可调吸收增强，并将创造新的光学物理和能量应用制度。结合垂直方向上更有效的载流子输运特性，这种增强光-物质相互作用机制的未开发潜力将在纳米腔增强的二维光电探测器和光伏器件中得到展示，从而显著提高功率转换效率。

AbstractNontechnical: Photodetector and photovoltaic devices are key components for converting light energy to electricity. To evaluate the performance of these devices, power conversion efficiency is one of the most important parameters, describing how much light energy is converted to electricity. Due to the advances of two-dimensional materials in recent years, it is believed that revolutionary ultra-thin optoelectronic devices are possible. However, because of the weak light absorption within these atomically thin layers, the power conversion efficiency of two-dimensional-material-based photodetector and photovoltaic devices is low. Therefore, it is essential to design and develop new strategies to improve the power conversion efficiency of these two-dimensional energy harvesting devices. This project will combine electrical (i.e. vertical carrier transport) and optical (i.e. Nano-cavity) architectures to overcome this grand challenge. (1) Since the transport distance of electrons and holes is only a few nanometers, the carrier transport efficiency is superior compared with their bulk counterparts. (2) The Nano-cavity structure significantly enhances the optical absorption within these two-dimensional layers due to strong optical interference resonances. Therefore, the power conversion efficiency can be increased drastically. This EAGER program will perform a combined fundamental and experimental investigation to validate this scientific hypothesis, which will pave the way towards the development of practically high-efficiency two-dimensional photo-harvesting devices. Technical: In most thin-film energy harvesting/conversion applications, there is a long-existing trade-off between optical absorption and thickness of semiconductor materials. It is particularly true in recently emerging two-dimensional-material-based optoelectronic photodetector and photovoltaic devices. Due to the atomically thin layers, their light-matter interactions (e.g., optical absorption and energy conversion enfficiency) are weak. Consequently, absorption enhancement strategies will introduce revolutionary advances to these two-dimensional-based light-harvesting devices. On the other hand, it is generally believed that minimizing the volume of active material can suppress the noise and thermal excess carriers in the diffusion-limited operating mode for photodetectors. It can also minimize the recombination of carriers in photovoltaic devices. However, this advantage is only viable in the vertical device architecture where carriers flow along the vertical direction and dominated by out-of-plane quantum tunneling. In this project, we will develop a fundemantal strategy to enhance the light-matter interaction of two-dimensional-materials based on strong interference effect in planar nanocavities, and overcome the limitation between the optical absorption and film thickness for energy harvesting devices. This principle is quite general and will be applied to explore the spectrally tunable absorption enhancement of various absorptive two-dimensional materials and will create new regimes of optical physics and energy applications. Combined with more efficient carrier transport properties along the vertical direction, the untapped potential of this mechanism for enhanced light-matter interaction will be demonstrated in Nano-cavity enhanced two-dimensional photodetector and photovoltaic devices with significantly improved power conversion efficiency.