Proceedings of nanoGe Fall Meeting19 (NFM19)
DOI: https://doi.org/10.29363/nanoge.nfm.2019.106
Publication date: 18th July 2019
Blend films of conjugated polymers (p-type donor polymer and n-type acceptor polymer) have gained increasing attention as a photovoltaic layer for polymer solar cells.[1] Photovoltaic performances of the blend film critically depend on the charge (hole and electron) transport within the film, which is influenced by the crystallization, aggregation, and phase separation of the constituent conjugated polymers. The electrical conductivity and mobility of the blend film have been evaluated by macroscopic current density-voltage measurement. However, there is a large gap between the insights that could be derived from the bulk-averaged conducting properties and those about local conductive features which are subject to the nanoscale morphologies of the blend film. Thus, in-depth understanding of the local conductive property of the blend films is required for designing materials to give efficient charge transport toward the improvement of the photovoltaic performance.
In this study, we apply conductive atomic force microscopy (C-AFM) as a tool for studying the local conductive properties of conjugated polymer blend films on a scale of nanometers. First, we employed C-AFM to characterize the local hole conductivity of the donor/acceptor polymer blend film. We discussed the existence of an intermixed region that was located between donor-rich and acceptor-rich domains, via observed hole current images.[2] The restricted charge-transport of the intermixed region found to be closely related to the device photovoltaic performance.[3] Second, we developed a method to measure electron current through acceptor polymers by using air-stable low work function electrode that is prepared by coating ethoxylated polyethyleneimine as a surface modifier on to indium-tin-oxide electrode. With this electrode, electron-transport network formed in donor/acceptor polymer blends can be successfully observed as well as hole-transport network is characterized.[4] Our approach based on C-AFM to electrically resolve nanostructures of conjugated polymer blends contributes to further understanding of the mechanisms for excellent charge transport and creation of photovoltaic functions of polymer solar cells composed of donor and acceptor polymers.
This work was supported by the JSPS KAKENHI Grant Number JP19H02789, the CREST program of the Japan Science and Technology Agency Grant Number JPMJCR12C4, the Kansai Research Foundation for technology promotion, and Murata Science Foundation.
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