Effect of the Type and Number of Organic Addends on Fullerene Acceptors for n‐Type Electronic Devices: Redox Properties and Energy Levels

Abstract

AbstractFullerenes are still among the best performing electron acceptor materials for electronic applications such as organic solar cells, organic‐inorganic perovskite solar cells and transistors. We demonstrate that voltammetry is a very powerful tool for the determination of the redox potentials and thus the LUMO levels of various fullerene acceptor materials when identical conditions, i. e. same electrolyte, electrode material and potential standard, are used. The analyzed fullerene derivatives bear several types (indene, anthracene and 1,2‐dimethoxymethano groups) and numbers (mono‐, bis‐ and tris‐adducts) of addends. Our systematical study enables a direct correlation of the values obtained for the individual fullerenes, and a linear relationship of the redox potential and the number of addends was found. The high lying LUMO levels of the bis‐ and tris‐adducts are favorable in terms of a high open circuit voltage in combination with polymer donors in bulk heterojunction solar cells. Considering only high LUMO values IC60TA and IC70TA are the most promising materials for organic solar cells revealing a high VOC. The bis‐adducts of the fullerenes reveal LUMO levels that closely match the energy level of the widely used organometal trihalide CH3NH3PbI in perovskite solar cells.