Acid vapor-induced enhanced electrical current rectification in phenothiazine-based electronic devices

Engineering transformable electronic features in two-terminal molecular junctions is of significant interest for advancing molecular-scale electronics. We demonstrate external stimuli (acid vapor)-responsive enhanced electrical current rectification (so called diode) in phenothiazine-based (R1) vertically stacked molecular junctions (MJs) with a configuration of p⁺-Si/R1_{58 nm}/ITO. The fabricated junctions exhibit nearly 530% enhancement in the electrical current rectification ratio (RR) in response to acid-vapor exposure for 60 seconds. The electronic functions of the devices can be partially set back using triethylamine (a weak base) vapor. Exposure to acid vapor forms cation radicals, (R1˙⁺)H⁺, that bring the lowest unoccupied molecular orbital (LUMO) closer to the Fermi level (<i>E</i> _F) of the ITO electrode in forward bias. In contrast, alignment of the highest occupied molecular orbital (HOMO) is not favorable under reverse bias conditions, which causes the emergence of the rectification ratio in the acid-exposed MJs. Electrical impedance spectra reveal a high charge transfer resistance (<i>R</i> _ct) of about 6 MΩ in pristine MJs, behaving like a resistor. However, the acid vapor facilitates an enhanced current flow at the forward bias compared to that at the reverse bias, mimicking diode functionality. The molecular junctions scrutinized for alternating current (AC) to direct current (DC) conversion using a function generator exhibit optimal diode performance at 500 Hz. Our findings demonstrate a method for high-yield device fabrication (∼86% working devices) that can be utilized for acid- and base-vapor-facilitated transformable electronic functions mimicking traditional electronics.