(Invited) Novel Pyridine-functionalized Fullerene Derivatives toward the Efficient and Hysteresis-free Perovskite Solar Cells

Abstract

Fullerene derivatives with strong electron-accepting abilities have been extensively used as electron transport layers (ETLs) of inverted (p–i–n) planar heterojunction perovskite solar cells (iPSCs); however the effect of the alkyl chains and a specific heteroatom site within the fullerene derivative on its electron transport properties has scarcely been studied. Herein,by employing pyridine carboxaldehydes bearing nitrogen sites within the pyridine moiety as a reactant, a series of novel pyridine-functionalized fullerene derivatives with variable nitrogen sites and alkyl chains length were synthesized facilely via a one-step 1, 3-dipolar cycloaddition reaction, and their molecular structures as well as molecular packing were unambiguously determined by X-ray single crystal diffraction. Despite that fullerene derivatives exhibit negligible difference in the molecular energy level and optical absorption, however, their electron transport properties are found to sensitively depend on the length of alkyl chains and nitrogen sites within the pyridine moiety. The C60-3-Py-based device shows the highest power conversion efficiency (PCE) of 17.57%. The discrepancy of the electron transport properties of fullerene derivatives is primarily due to the difference in the coordination interaction between the pyridine moiety and the Pb2+ ion of the MAPbI3 perovskite layer interaction between the pyridine moiety and the Pb2+ ion of the MAPbI3 perovskite layer.