Tuning of Interfacial Charge Transport in Organic Heterostructures via Aryl Electrografting for Efficient Gas Sensors.

Modulation of interfacial conductivity in organic heterostructures is a highly promising strategy to improve the performance of electronic devices. In this endeavor, the present work reports the fabrication of a bilayer heterojunction device, combining octafluoro copper phthalocyanine (CuF8 Pc) and lutetium bis-phthalocyanine (LuPc2 ) and tunes the charge transport at the Cu(F8 Pc)-(LuPc2 ) interface by aryl electrografting on the device electrode to improve the device NH3 -sensing properties. Dimethoxybenzene (DMB) and tetrafluoro benzene (TFB) electrografted by an aryldiazonium electroreduction method form a few-nanometer-thick organic film on ITO. The conductivity of the heterojunction devices formed by coating a Cu(F8 Pc)/LuPc2 bilayer over the aryl-grafted electrode strongly varies according to the electronic effects of the substituents in the aryl. Accordingly, DMB increases while TFB decreases the mobile charges accumulation at the Cu(F8 Pc)-(LuPc2 ) interface. This is explained by the perfect alignment of the frontier molecular orbitals of DMB and Cu(F8 Pc), facilitating charge injection into the Cu(F8 Pc) layer. On the contrary, TFB behaves like a strong acceptor and reduces the mobile charges accumulation at the Cu(F8 Pc)-(LuPc2 ) interface. Such interfacial conductivity variation influences the device NH3 -sensing properties, which increase because of DMB grafting and decrease in the presence of TFB. DMB-based heterojunction devices contain four times higher active sites for NH3 adsorption and could detect NH3 down to 1 ppm with limited interference from humidity, making them suitable for real environment NH3 detection.