Collaborative Research: Nanostructured Conductive Tin Oxide for High-Efficiency Light Trapping in Thin Films and Photonic Devices

该项目由材料研究部（DMR）的电子和光子材料计划（EMT）以及电气，通信和网络系统部（ECCS）的电子，光子学和磁器件计划（EPMD）共同资助。非技术描述：本计画研究奈米结构导电性二氧化锡作为自组装电极，应用于以薄膜及二维材料为基础之光子元件中，以达到高效率之光捕捉。这些纳米结构将入射光散射到活性吸收体材料的平面中，从而“捕获”光，以用于在纳米吸收体中强烈增强光学吸收。与基于晶圆的光电器件相比，该技术能够大幅降低材料消耗和成本。它具有广泛的潜在应用，从红外传感/成像到能量收集，包括将热量直接转换为电能。光吸收器中的光捕获也使一组新的灵活，高效的光子器件能够安装在曲面上。该项目为研究生和本科生提供了广泛的前沿研究经验。该团队还参加了波士顿科学博物馆的“共享科学研讨会和实习”，演示了光捕获效应，让参观者用肉眼观察原子级薄的石墨烯层。PI（刘）将从这个研究项目中产生的新概念整合到达特茅斯学院为高中三年级和四年级学生举办的夏季工程研讨会中。合作研究者（孔）参与麻省理工学院埃杰顿中心，以启发K-12学生使用研究中产生的纳米结构材料。技术描述：本项目研究光子器件中的高效、低损耗光捕获。目标是研究纳米结构导电氧化锡SnOx（x2）作为低温（250摄氏度）自组装电极，用于基于薄膜和二维材料的光子器件中的高效光捕获，从而大大提高其量子效率。由于非化学计量，过量的Sn在退火时偏析并诱导纳米块/纳米针形成。为了实现高的光捕获效率，该团队研究了纳米结构形成，双极导电以及SnOx和薄膜/2D吸收体之间的纳米级光学耦合的基本原理。基于通过该项目获得的新知识，可以针对不同的应用优化器件结构和制造工艺。两个例子是（a）用于热光伏电池和红外传感器的Ge和GeSn薄膜中的SnOx增强的光捕获，以及（B）用于光子器件的SnOx/2D材料异质结构。这项研究可能会导致一类新的低损耗，纳米结构的导电氧化物，用于在薄的有源吸收体中高效捕获光，厚度从单个原子层到几微米。与传统的表面纹理透明导电氧化物相比，这种新技术提高了光捕获效率的吸收器，并同时最大限度地减少了表面漏电流。

This project is jointly funded by the Electronic and Photonic Materials Program (EPM) in the Division of Materials Research (DMR), and by the Electronics, Photonics, and Magnetic Devices Program (EPMD) in the Division of Electrical, Communications and Cyber Systems (ECCS). Nontechnical Description: This project investigates nanostructured conductive tin oxide as a self-assembled electrode for high-efficiency light trapping in photonic devices based on thin films and two-dimensional (2D) materials. These nanostructures scatter the incident light into the plane of the active absorber materials, thereby "trapping" the light for strongly enhanced optical absorption in ultrathin absorbers. This technology enables a drastic reduction in materials consumption and cost compared to wafer-based optoelectronic devices. It has broad potential applications from infrared sensing/imaging to energy harvesting, including direct conversion of heat into electricity. The light trapping in ultrathin absorbers also enables a new group of flexible, high-efficiency photonic devices that can be installed on curved surfaces. The project provides a broad range of cutting-edge research experiences for graduate and undergraduate students. The team also participates in the "sharing science workshop and practicum" at the Museum of Science in Boston to make demos on the light trapping effect that allows visitors to observe an atomically thin graphene layer with naked eyes. The PI (Liu) integrates the new concepts generated from this research project into the Summer Engineering Workshop at Dartmouth College for high-school juniors and seniors. The Co-PI (Kong) participates in the MIT Edgerton Center to inspire K-12 students using the nanostructured materials produced in the research.Technical Description: This project studies high-efficiency, low-loss light trapping in photonic devices. The goal is to investigate nanostructured conductive tin oxide SnOx (x2) as a low-temperature (250 degrees Celsius) self-assembled electrode for efficient light trapping in thin-film and 2D-materials based photonic devices, thereby greatly enhancing their quantum efficiencies. Due to the non-stoichiometry, the excess Sn segregates upon annealing and induces nanobrick/nanoneedle formation. In order to achieve high light trapping efficiency, the team studies the fundamentals of the nanostructure formation, ambipolar electrical conduction, and nanoscale optical coupling between SnOx and thin film/2D absorbers. Based on the new knowledge gained through this project, the device structure and fabrication process can be optimized for different applications. Two examples are (a) SnOx enhanced light trapping in Ge and GeSn thin films for thermo photovoltaic cells and infrared sensors, and (b) SnOx/2D material heterostructures for photonic devices. The research can potentially lead to a new class of low-loss, nanostructured conductive oxides for high efficiency light trapping in thin active absorbers with thicknesses ranging from a single atomic layer to a few micrometers. Compared to conventional surface-textured transparent conductive oxides, this new technology enhances light trapping efficiency for ultrathin absorbers and minimizes the surface leakage current simultaneously.