Contemporary Impedance Analyses of Archetypical PM6:Y6 Bulk-Heterojunction Blend

Abstract

An organic bulk heterojunction based on a blend of a conjugated polymer PBDB-T-2F (PM6) and a non-fullerene acceptor BTP-4F (Y6) has come forward in recent years as an archetypical system for the study of the operating principles of organic photovoltaic devices. One of the experimental techniques that has shown immense value in the study of this blend is impedance spectroscopy (IS). In spite of its relative simplicity, this method and its derivatives offer the possibility of diverse, all-round characterization of materials and devices of interest. This Perspective summarizes recent research demonstrating the application of IS as a powerful method to obtain multifaceted information on PM6:Y6 and presents a current understanding of the experimental results. A description of general approaches employed in the processing of experimental data, including the Nyquist plots, capacitance spectra, and energy-resolved electrochemical IS data, is supplemented by additional analysis, notably on characterization of non-geminate recombination of free charge carriers and their transport in this groundbreaking organic blend. Finally, this work outlines the perspectives and limitations of IS in the study of future promising materials and devices.