In-Depth\nStudy of Ambipolar Charge-Transport Regime\nthrough External Triggers and Gas Sensing

Ambipolar\ndevices are a hot topic in research tables due to their\nunique advantage in reducing the size of the electrical system and\nenhancing its efficiency. Here, we report a bilayer heterojunction\ndevice constructed using octafluoro–vanadyl–phthalocyanine\n(VOF<sub>8</sub>Pc) and lutetium bisphthalocyanine (LuPc<sub>2</sub>), which exhibits both p- and n-type behaviors under oxidizing (NO<sub>2</sub> and O<sub>3</sub>) and reducing gas (NH<sub>3</sub>) species\ndepending on the humidity level and temperature variations. The initial\npolarity of the device is identified as n-type by measuring a current\ndecrease under oxygen exposure. Most interestingly, we were capable\nof observing the zero state (no response) where both opposite charge\ncarriers fight for the majority to dominate the electrical properties\nof the device when it goes from n- to p-type or vice versa. The inversion\nin the nature of the majority charge carriers in this ambipolar device\nwas achieved by optimizing the external trigger. The unique property\nof controllable polarity inversion in a VOF<sub>8</sub>Pc/LuPc<sub>2</sub>-based bilayer heterojunction device makes it the most effective\nambipolar device for real-world applications.