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

Abstract

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 (CuF 8 Pc) and lutetium bis-phthalocyanine (LuPc 2 ) and tunes the charge transport at the Cu(F 8 Pc)-(LuPc 2 ) interface by aryl electrografting on the device electrode to improve the device NH 3 -sensing properties. Dimethoxybenzene (DMB) and tetrafluoro benzene (TFB) electrografted by an aryldiazonium electroreduction method form a fewnanometer-thick organic film on ITO. The conductivity of the heterojunction devices formed by coating a Cu(F 8 Pc)/LuPc 2 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(F 8 Pc)-(LuPc 2 ) interface. This is explained by the perfect alignment of the frontier molecular orbitals of DMB and Cu(F 8 Pc), facilitating charge injection into the Cu(F 8 Pc) layer. On the contrary, TFB behaves like a strong acceptor and reduces the mobile charges accumulation at the Cu(F 8 Pc)-(LuPc 2 ) interface. Such interfacial conductivity variation influences the device NH 3 -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 NH 3 adsorption and could detect NH 3 down to 1 ppm with limited interference from humidity, making them suitable for real environment NH 3 detection.