Development of fullerene derivatives with high LUMO level through changes in π-conjugated system shape

Abstract

This article describes a concept for designing fullerene-based electron-accepting materials to obtain high open-circuit voltage (V OC) in organic thin-film photovoltaic devices without an accompanying decrease in short-circuit current density. The keys to this concept are (1) reducing the size of the fullerene π-conjugated system to realize high V OC and (2) shortening the inter-fullerene distance in the solid-state packing structure to achieve high short-circuit current density (J SC), which is made possible by well-designed supramolecular organization or a small organic addend. In this article, two representative examples are discussed. One is 1,4-bis(silylmethyl)[60]fullerene (SIMEF), which forms a columnar fullerene-core array for high electron mobility and undergoes thermal crystallization for good phase separation with the electron-donating material. The other is a 56π-electron fullerene derivative bearing a dihydromethano group, the smallest carbon addend, which does not disrupt fullerene–fullerene contact in the solid state.