Charge Transfer and Ultrafast Nonlinear Optical Properties above Percolation Threshold in Graphene-Induced ZnTTBPc

Abstract

Electrically conducting matrix comprised of graphene and organic molecule is immensely versatile and has a broad range of potential applications. Highly soluble zinc tetra-tert-butyl phthalocyanine−reduced graphene oxide (ZnTTBPc−RGO) blend samples have been synthesized with different RGO concentrations (0−1 volume fraction). The electrical conductivity of ZnTTBPc−RGO samples indicates a percolating behavior with the three-dimensional percolation threshold of ∼0.167 vol. fraction of RGO. Room temperature as well as temperature dependent (100−320 K) photosensitivity (P) measurements go through a maximum at ∼0.33 vol. fraction of RGO content (namely sample G). Calculated P values exhibit a decreasing trend with increasing temperature and have been ascribed to enhanced scattering mechanisms. Resistivity data suggest that the charge transport process of ZnTTBPc− RGO is consistent with Efros−Shklovskii variable range hopping mechanism at 88−320 K. Moreover, comprehensive measurements on nonlinear absorption (NLA) of ZnTTBPc−RGO show a significant enhancement in nonlinear optical properties compared to pure ZnTTBPc when measured with ∼100 fs, 1 kHz laser pulse at 540 nm in an intensity range of 37−130 GW/cm 2 . Comparative measurements on P and NLA coefficient show highest values for sample G compared to others along with faster electron transfer rate, confirmed by femtosecond transient absorption spectroscopy measurements. These results provide a way of characterizing ZnTTBPc−RGO blend for optoelectronic device applications.