A wide solar spectrum utilization and fast charge carrier transport upon variable GaAs interlayer thickness in ZnPc/GaAs/ZnPc hybrid thin-film structures

Abstract

The effects of inorganic layer thickness on the photophysical properties of the organic layer in an organic-inorganic hybrid system were investigated in this paper. Photosensitive Zinc Phthalocyanine (ZnPc) and GaAs layers were alternatively stacked through simple physical vapor deposition, and the impact of GaAs layer thickness was explored through structural, optical, and electrical characterization techniques. The strain-induced quantum size effect was evident in the hybrid structure, and it was confirmed in Raman analysis with broad vibration peaks of the GaAs phase, which resulted in a decrease in the GaAs thickness < Bohr radius (RB). In addition, a complementary absorption edge was obtained at 295 nm along with ZnPc absorption features, but GaAs failed to contribute to spectral absorption with its thickness > RB. The decreased photoluminescence intensity and fluorescence decay time of ZnPc after incorporation of GaAs imply that charge transfer from ZnPc to GaAs occurs quickly. The transient photocurrent measurement demonstrates that the current density of hybrid film with GaAs thickness < Bohr radius was significantly increased. As expected, the GaAs with thickness above the Bohr radius is ineffective for improving the photocurrent. Impedance spectroscopy analysis was applied to explore the electrical transport behavior in the hybrid system using a two-electrode system. An ultra-thin GaAs layer noticeably promoted mass transfer at the ZnPc-GaAs interface and increased the conductivity of the hybrid system with the least charge transfer resistance.