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

Fullerene (C-60) and multilayer graphene hybrid devices were fabricated using electrophoretic deposition, where the C-60 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 A(2g) mode of the C-60 molecules at similar to 1453 cm(-1), while blue shifts of and similar to 17 cm(-1) were 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 I-2D/I-G (hybrid) dropped to similar to 0.18 from similar to 0.3 (bare graphene), and this reduction in I-2D/I-G is also a signature of hole-doped graphene, consistent with the relatively strong electron accepting nature of C-60. 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 similar to 5.8 K. Additionally, a low energy shift in the Fermi level, E-F approximate to 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 a wavelength lambda ranging from similar to 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 similar to 10(9) A/W at lambda approximate to 400 nm and similar to 298 K, while the detectivity and external quantum efficiency were also exceptional, similar to 10(15) jones and similar to 10(9)%, respectively, at similar to 1 V and a light power density of similar to 3 mW/cm(2). The R values are, similar to 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 photoresponse of the C-60-graphene hybrids reported here is attributed to the doping enhancement arising in graphene upon the adsorption of C-60. This work demonstrates the exceptional potential of such hybrid nanocarbon-based structures for optoelectronics.