Aziridine-functionalized graphene: Effect of aromaticity for aryl functional groups on enhanced power conversion efficiency of organic photovoltaic cells

Abstract

We have demonstrated the covalent functionalization of graphene by nitrene chemistry, resulting in highly dispersed aryl azides functionalized graphene. Two different ortho-substituted aryl azides having different aromatic ring (π-conjugation) and ester/anhydride substituent have been synthesized. Further, on thermolysis they undergo [2+1] cycloaddition ensuing in the formation of aziridine adduct with sp2 carbons of graphene. Resulting aryl azide functionalized graphene sheets (f-graphene I & II) are soluble in most common organic (polar and non polar) solvents, facilitating the structural/property characterization and the device fabrication by solution processing. The aziridine linkage modification of the π conjugation and the strong electronic interaction between the f-graphenes and poly (3-hexylthiophene) (P3HT):Phenyl-C61-Butyric-Acid-Methyl Ester (PCBM) has been confirmed by various spectroscopic analysis. The implications of changing the aromaticity of the aryl azides attached to f-graphenes on the P3HT:PCBM bulk heterojunction (BHJ) photovoltaic device are discussed. The solution cast f-graphene I (5%) doped P3HT:PCBM BHJ showed the power conversion efficiency ɳ = 1.94( ± 0.06) %, while f-graphene II (5%) doped exhibited ɳ = 2.16( ± 0.07) % under AM 1.5 illumination (100 mW/cm2), which is found to be more than double the efficiency of the reference cell. Keywords: Aryl azide, Aromatic functionalization, Soluble graphene, Photovoltaic, Power conversion efficiency