Bias Induced Ambipolar Transport in Organic Heterojunction Sensors

Abstract

Interface engineering in organic heterostructures is an important approach to tuning the characteristics of organic electronic devices and improving their performances in applications, such as gas sensing. Herein, organic heterostructures containing, a polyporphine (pZnP-1), perfluorinated copper phthalocyanine (Cu(F₁₆Pc)), and lutetium bis-phthalocyanine (LuPc₂) are synthesized by a combination of electrochemical and PVD methods for investigation of charge transport and ammonia (NH₃) sensing application. pZnP-1 is synthesized by controlled oxidative electropolymerization and reveals a rough surface, which influences the electrical nature of its interface with the phthalocyanine. The electrical properties of the heterojunction devices reveal distinct interfacial and bulk charge transport properties, which are modulated by the thickness of pZnP-1 and the external electric field. Indeed, the heterojunction device containing a thin film of pZnP-1 displays n-type behavior at low bias and p-type nature at higher bias; i.e., an ambipolar behavior, in which ambipolarity is triggered by the external electric field. On the other hand, the heterojunction device having a thick film of pZnP-1 exhibits p-type behavior at all the studied biases. Investigation of NH₃ sensing properties of the heterojunction devices highlights the advantages of introducing pZnP-1 in the heterostructures, which enhances the sensitivity, stability, repeatability, and humidity tolerance of the sensors.