Amorphization enhances long-range tunneling in organic nanofilms

Metal Phthalocyanine-based materials are known for their stability and are widely used in flexible organic electronics. The study presented here investigates the impact of substrate temperature on the growth to control the crystallinity of the deposited copper phthalocyanine (CuPc) thin films on silicon substrates and its effect on the charge transport in Au/CuPc/n-Si heterostructures. Current-voltage (I-V) characterization of the heterostructures reveals the appearance of multiple transport mechanisms, ranging from direct and Fowler-Nordheim tunneling at lower temperatures to Poole-Frenkel conduction at higher temperatures, depending on the crystallinity of the deposited CuPc films. Resonant tunneling observed in the amorphous thin film suggests the existence of a π-electron bridge parallel to the vertical charge transport path. Such orientation of CuPc molecules is important for efficient charge extraction in organic solar cells.