Impact of a polystyrene-based passivating interlayer on hybrid polymer/ZnO nanowire heterojunctions

To improve the quality of hybrid p-polymer/n-zinc oxide (ZnO) nanowire heterojunctions a thin polystyrene (PS)-based passivating interlayer is deposited on plain aqueous-chemically grown ZnO nanowires by spin coating. The structural investigation of the PS-coated nanowires via scanning electron microscopy shows that the concentration of PS in the solution affects the thickness of the PS layer. For vertically aligned nanowires a concentration of 0.125 g in 10 ml toluene is needed to get thin homogeneous passivating layers. Photoluminescence measurements of the PS-coated nanowires show a decrease of the deep-level emission depending on the PS concentration which indicates a passivation on the nanowire surface without affecting the general optical properties of the ZnO. Current-voltage characteristics of these samples show a decreased hysteresis and an increased current with decreasing PS concentration/PS layer thickness. However, a reasonably thin layer reduces the tunnelling through trap states of the ZnO nanowires.