Highly Selective and Scalable Fullerene-Cation-Mediated Synthesis Accessing Cyclo[60]fullerenes with Five-Membered Carbon Ring and Their Application to Perovskite Solar Cells

Cyclo[60]fullerenes are widely used in many applications including photovoltaic devices owing to their high electron affinity and mobility for an organic molecule. However, their synthesis has been limited to certain derivatives with low yields. In this work, a fullerene-cation-mediated synthesis, accessing a new class of five-membered carbon ring cyclo[60]fullerenes with high yields of up to 93% is showcased. This method utilizes aryl[60]fullerene cations, ArC60+, as intermediates, which are generated in situ by heating the aryl[60]fullerenyl dimers in the presence of CuBr2. In addition, five-membered carbon ring cyclo[60]fullerenes display excellent device applicability when they are used in perovskite solar cells as over-coating layers of electron-transporting layers. A power conversion efficiency of 20.7% is achieved owing to the favorable energy alignment, optimized substrate design, and electrochemical stability of the five-membered carbon ring fullerenes.