ИСТИНА

Highly soluble fullerene derivatives with two or more fullerene cages are of particular interest as prospective acceptor materials for design of stable photovoltaic devices with improved morphology and charge transport properties. Recently it was demonstrated that photoelectric characteristics of nalkyl ethers of double-caged fullerene derivatives nonmonotonically correlates with alkyl chain length [1]. Highest photovoltaic performance was found for solar cells based on the C9 and С10-alkyl ethers whereas the devices based on C8 and C18-alkyl ethers unexpectedly revealed two-fold PCE drop. However, the photovoltaic properties of C7, C11–C17 alkyl ethers have not been studied. Here we report a series of novel highly soluble double-caged fullerene derivatives with C7, C11, C13, C14, and C15-alkyl groups in the ester function and their effect on photovoltaic performance of solar cells based thereon. Novel double-caged fullerene derivatives have been prepared through lithium salt-assisted [2+3]- cycloaddition of azomethine ylides generated from glycine esters and paraformaldehyde [1]. Synthesized compounds were LC isolated as individual compounds with 95+% purity and characterized by MALDI mass-spectrometry and NMR spectroscopy. Optical and electronic properties of novel double-caged fullerene derivatives have been studied by UV/Vis-spectroscopy and cyclic voltammetry. The effect of alkyl moiety on solubilities of double-caged fullerene derivatives is discussed. Novel double-caged fullerene derivatives were tested as an acceptor material in P3HT-based organic solar cells and demonstrated strong dependence of PCE on the length of the alkyl moiety. The morphology of the active layer was studied by microscopy methods. The effect of alkyl chain length in double-caged fullerene derivatives on their solubility, morphology and photoelectric characteristics (series and shunt resistances and short-circuit current density) is discussed.