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

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/cm². 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.