Tunneling of charge carriers across a gold–squaraine interface

• Injection and extraction of holes across gold–squaraine interface were studied.
• Contact resistances for injection and extraction of holes are different.
• Interface dipole facilitates holes injection and aggravates holes extraction.

We describe the transfer of holes across a gold–squaraine–gold structure via two distinct processes describing tunneling of holes through the injecting and extracting interfaces, respectively. Such separation in two steps was achieved through the evaluation of the contact resistances, derived from a decomposition of the measured total current–voltage characteristic into the corresponding components. Using the Simmons approximation, we determined the height Φ and the width d of the tunneling barrier existing at gold–squaraine interface. Interestingly, for a given gold–squaraine interface, the values of Φ and d differed for injection and extraction of holes across this interface. We attribute this difference to the action of permanent dipoles present at this interface.