Single-gate graphene thermopiles enabled by locally Al-modified graphene legs on PET substrates

We report a simplified graphene thermopile architecture fabricated on PET substrates. Conventional single-material graphene thermopiles typically require independent electrostatic control of the two thermoelectric legs, increasing both fabrication complexity and device footprint. Here, one graphene leg is locally modified by an Al overlayer, while the overall carrier density is tuned using a single global ionic-liquid gate. As a reference, graphene/Au thermopiles exhibit the expected linear scaling of thermovoltage with the number of thermocouples, but their output remains limited by the small thermopower of Au. In contrast, the Al-covered graphene leg generates a large, weakly gate-dependent negative thermovoltage contribution while preserving graphene-dominated transport, thereby enhancing the thermoelectric contrast with the uncovered graphene leg. Consequently, graphene/Al-covered graphene thermopiles exhibit a substantially higher output voltage, which increases approximately linearly with thermocouple number and surpasses that of the graphene/Au reference structure. These results establish local Al-induced electronic modification as a simple and scalable strategy for realizing graphene thermopiles without multiple local gates, providing a device platform compatible with flexible and transparent polymer substrates.