Ambipolar Heterojunction Sensors: Another Way to Detect Polluting Gases

Abstract

Gas sensors based on ambipolar materials offer significant advantages in reducing the size of the analytical system and enhancing its efficiency. Here, bilayer heterojunction devices are constructed using different octafluorinated phthalocyanine complexes, with Zn and Co as metal centers, combined with a lutetium bisphthalocyanine complex (LuPc₂). Stable p-type behavior is observed for the ZnF₈Pc/LuPc₂ device under both electron-donating (NH₃) and -oxidizing (NO₂ and O₃) gaseous species, while the CoF₈Pc/LuPc₂ device exhibits n-type behavior under reducing gases and p-type behavior under oxidizing gases. The nature of majority of the charge carriers of Co-based devices varies depending on the nature of target gases, displaying an ambipolar behavior. Both heterojunction devices demonstrate stable and observable response toward all three toxic gases in the sub-ppm range. Remarkably, the Co-based device is highly sensitive toward ammonia with a limit of detection (LOD) of 200 ppb, whereas the Zn-based device demonstrates exceptional sensitivity toward oxidizing gases, with excellent LOD values of 4.9 and 0.75 ppb toward NO₂ and O₃, respectively, which makes it one of the most effective organic heterojunction sensors reported so far for oxidizing gases.