Multi-Modal Spectroscopic and Microscopic Characterization of Thin-Film Networks of Semiconducting Carbon Nanotubes

Abstract

Thin-film distributions of semi-conducting carbon nanotubes (CNTs) exhibit potential as a candidate material for photovoltaic devices due to their strong absorption throughout the solar spectrum and exceptional transport properties. Despite this potential, characterization of the systemic parameters which determine and limit photovoltaic performance has remained a challenge. To this end, multidimensional spectroscopic methods represent a valuable tool in identifying and describing the energetic pathways in these systems which contribute to device performance. In this presentation, we demonstrate the development of a broad bandwidth (500-1300 nm), high-repetition rate (100 kHz) 2-dimenstional electronic spectroscopy (2D-ES) system capable of high-speed, low noise spectroscopic characterization of the energy transfer pathways. The diagonal and cross-peaks measured in 2D-ES measurements provide critical information about the dephasing time, correlation, and couplings between electronic states. The high acquisition rate of our measurement system enables us to monitor multiple detection pathways, limited not only to optical absorption, but also measurement of the photo-induced current allowing for direct spectroscopic characterization of the energy pathways taken by carriers contributing to photocurrents. In addition to traditional far-field spectroscopic characterization, in which the response of a macroscopic area (10's of μm2) is collected, we further show the use of our broadband source in microscopic spatial mapping of device response. Through combination with atomic force microscopy of the nanoscopic structure of a surface, we demonstrate the ability to characterize and correlate the topology of a surface with a specific optical response.