Dramatic Enhancement of Optoelectronic Properties in Electrophoretically Deposited C60-Graphene Hybrids.

Abstract

Fullerene (C60) and multi-layer graphene hybrid devices were fabricated using electrophoretic deposition, where the C60 clusters are electrically charged upon the application of an external bias in a polar solvent, acetonitrile, mixed with toluene, which facilitates their deposition on the graphene membranes. Raman spectroscopy unveiled the unique vibrational fingerprints associated with the A2g mode of the C60 molecules at ~ 1453 cm-1, while a blue-shift of ~ 6 cm-1 and ~ 17 cm-1 was also attributed to the G- and 2D-bands of the hybrids relative to bare graphene, suggestive of p-doped graphene. The intensity ratio of the G- and the 2D-bands I2D/IG (hybrid) dropped to ~ 0.18 from ~ 0.3 (bare graphene), and this reduction in I2D/IG is also a signature of hole-doped graphene, consistent with the relatively strong electron accepting nature of C60. The electronic conductance of the two-terminal hybrid devices increased relative to bare graphene at room temperature which was attributed to the increased carrier density, and temperature-dependent electronic transport measurements were also conducted from ambient down to ~ 5.8 K. Additionally, a low energy shift in the Fermi level EF ~ 140 meV was calculated for the hybrids. When the hybrid devices were irradiated with a broadband white light source and a tunable laser source (with wavelength λ ranging from ~ 400-1100 nm), a strong photoresponse was evident, in contrast to the bare graphene devices which appeared unresponsive. The responsivity ℛ of the hybrids was measured to be ~ 109 A/W at λ ~ 400 nm and ~ 298 K, while the detectivity and external quantum efficiency were also exceptional, ~ 1015 Jones and ~ 109 %, respectively at ~ 1 V and light power density of ~ 3 mW/cm2. The ℛ values are ∼ 10 times higher compared to other hybrid devices derived from graphene reported previously, such as quantum dot-graphene and few-layer MoS2-graphene heterostructures. The strong photo-response of the C60-graphene hybrids reported here is attributed to the doping enhancement arising in the graphene upon the adsorption of C60. This work demonstrates the exceptional potential of such hybrid nanocarbon-based structures for optoelectronics.