INVESTIGATING THE EFFECTS OF NANOSTRUCTURED DIELECTRIC LITHIUM FLUORIDE AND PLASMONIC GOLD INTERLAYERS IN ORGANIC PHOTOVOLTAICS, INCLUDING THE USE OF IN-SITU IMPEDANCE SPECTROSCOPY
Hasan Kurt
Materials Science and Engineering, PhD Dissertation, 2016
Thesis Jury
Assoc. Prof. Cleva W. Ow-Yang (Thesis Advisor), Prof. Dr. Yusuf Z. Menceloğlu, Assoc. Prof. Kürşat Şendur, Prof. Mustafa M. Demir, Asst. Prof. Çınar Öncel
Date & Time: August 1th, 2016 – 13.00 PM
Place: FENS G032
Keywords: organic photovoltaics, interface engineering, impedance spectroscopy, charge carrier dynamics, functional interfaces, plasmonic field enhancement
Abstract
Although tuning organic solar cell performance can be achieved by the design of nanostructured interlayers between the active layer and the anode, elucidating the actual photophysical effects of such buried interfaces during device operation is a challenge, for which impedance spectroscopy (IS) analysis offers pivotal insight. Herein we have used IS to distinguish the effects of two different nanostructured interlayers, with sol-LiF and sol-Au nanostructures, on the charge generation/recombination and charge transport/collection kinetics in bulk heterojunction organic solar cells in detail. IS analysis revealed that a more favorable energy alignment with the hole transport layer (HTL) improved charge collection efficiency in devices containing an ITO anode modified by sol-LiF, by facilitating charge transport and extraction through decreased charge carrier transit lifetime. In the case of a sol-Au interlayer between ITO and the HTL, IS analysis revealed that plasmonic field enhancement within the active layer improved charge generation, although the increase in mobile charge carriers did not impact charge transit dynamics significantly. Moreover, our work underscores a key advantage offered by IS analysis—instead of tracking the multivariate OPV device characteristics of fill factor and short-circuit current, one may obtain a more detailed analysis of the underlying operating mechanisms to elucidate the specific contributions of nanostructured interlayers.