Tightly Bound Double-Caged [60]Fullerene Derivatives with Enhanced Solubility: Structural Features and Application in Solar Cells

Victor A Brotsman; Vitaliy A Ioutsi; Alexey V Rybalchenko; Vitaliy Yu Markov; Nikita M Belov; Natalia S Lukonina; Sergey I Troyanov; Ilya N Ioffe; Vasiliy A Trukhanov; Galina K Galimova; Artur A Mannanov; Dmitry N Zubov; Erhard Kemnitz; Lev N Sidorov; Tatiana V Magdesieva; Dmitry Yu Paraschuk; Alexey A Goryunkov

doi:10.1002/asia.201700194

Tightly Bound Double-Caged [60]Fullerene Derivatives with Enhanced Solubility: Structural Features and Application in Solar Cells

Chem Asian J. 2017 May 18;12(10):1075-1086. doi: 10.1002/asia.201700194. Epub 2017 Apr 25.

Authors

Victor A Brotsman¹, Vitaliy A Ioutsi¹, Alexey V Rybalchenko¹, Vitaliy Yu Markov¹, Nikita M Belov¹, Natalia S Lukonina¹, Sergey I Troyanov¹, Ilya N Ioffe¹, Vasiliy A Trukhanov², Galina K Galimova², Artur A Mannanov², Dmitry N Zubov³, Erhard Kemnitz⁴, Lev N Sidorov¹, Tatiana V Magdesieva¹, Dmitry Yu Paraschuk², Alexey A Goryunkov¹

Affiliations

¹ Chemistry Department, Lomonosov Moscow State University, Leninskie Gory, 1-3, 119991, Moscow, Russia.
² Faculty of Physics & International Laser Center, Lomonosov Moscow State University, Leninskie Gory, 1-62, 119991, Moscow, Russia.
³ Institute of Nanotechnology of Microelectronics RAS, Leninsky Prospekt, 32A, 119991, Moscow, Russia.
⁴ Institut für Chemie, Humboldt Universität zu Berlin, Brook-Taylor-Strasse 2, 12489, Berlin, Germany.

PMID: 28281332
DOI: 10.1002/asia.201700194

Abstract

A series of novel highly soluble double-caged [60]fullerene derivatives were prepared by means of lithium-salt-assisted [2+3] cycloaddition. The bispheric molecules feature rigid linking of the fullerene spheres through a four-membered cycle and a pyrrolizidine bridge with an ester function CO₂ R (R=n-decyl, n-octadecyl, benzyl, and n-butyl; compounds 1 a-d, respectively), as demonstrated by NMR spectroscopy and X-ray diffraction. Cyclic voltammetry studies revealed three closely overlapping pairs of reversible peaks owing to consecutive one-electron reductions of fullerene cages, as well as an irreversible oxidation peak attributed to abstraction of an electron from the nitrogen lone-electron pair. Owing to charge delocalization over both carbon cages, compounds 1 a-d are characterized by upshifted energies of frontier molecular orbitals, a narrowed bandgap, and reduced electron-transfer reorganization energy relative to pristine C₆₀ . Neat thin films of the n-decyl compound 1 a demonstrated electron mobility of (1.3±0.4)×10^-3 cm² V^-1 s^-1 , which was comparable to phenyl-C₆₁ -butyric acid methyl ester (PCBM) and thus potentially advantageous for organic solar cells (OSC). Application of 1 in OSC allowed a twofold increase in the power conversion efficiencies of as-cast poly(3-hexylthiophene-2,5-diyl) (P3HT)/1 devices relative to the as-cast P3HT/PCBM ones. This is attributed to the good solubility of 1 and their enhanced charge-transport properties - both intramolecular, owing to tightly linked fullerene cages, and intermolecular, owing to the large number of close contacts between the neighboring double-caged molecules. Test P3HT/1 OSCs demonstrated power-conversion efficiencies up to 2.6 % (1 a). Surprisingly low optimal content of double-caged fullerene acceptor 1 in the photoactive layer (≈30 wt %) favored better light harvesting and carrier transport owing to the greater content of P3HT and its higher degree of crystallinity.

Keywords: X-ray diffraction; cage compounds; cyclic voltammetry; fullerenes; photochemistry.