Impedance spectroscopy analysis of the photophysical dynamics due to the nanostructuring of anode interlayers in organic photovoltaics

Although tuning organic solar cell performance can be achieved in 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-solution processed dielectric LiF (sol-LiF) and plasmonic Au (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 improved energy alignment with the hole transport layer (HTL) increased 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 enhancement within the active layer improved charge generation, although the increase in mobile charge carriers did not impact charge transit dynamics significantly. 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 elucidate the specific mechanisms contributed by the nanostructured interlayers. (C) 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim