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

Massachusetts Institute Of Technology, Cambridge MA

Investigators

Abstract

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 (x<2) 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.