Synthesis of 1,2-Dihydrofullerene Derivatives Using Lithium Acetylide and Their Performance in Organic Solar Cells

Abstract

Fullerene C₆₀ and C₇₀ derivatives with distinctly high LUMO levels compared to pristine fullerenes can be prepared by introducing two functional groups not at 1,4-position but at 1,2-position. In this work, we conducted reactions of C₆₀ with some lithium acetylides followed by nucleophilic substitutions with various alkyl iodides to give a series of soluble 1,2-dihydrofullerene derivatives in moderate yields. Then we fabricated the bulk-heterojunction (BHJ) solar cells using the 1,2-dihydrofullerene derivatives and poly(3-hexylthiophene) as the acceptor and the donor materials, respectively. These devices marked high open circuit voltage (Voc) of 0.58 – 0.60 V, which is comparable to that of a device using the benchmark acceptor, [6,6]-phenyl-C₆₁-butyric acid methyl ester (PCBM). We will discuss the characteristics of the BHJ solar cells using 1,2-fullerene derivatives in detail.