Array of Graphene Solar Cells on 100 mm Silicon Wafers for Power Systems

Graphene's outstanding conductivity and transparency make it an excellent candidate for photovoltaic applications. In this study, we designed and fabricated an array of graphene-based Schottky junction solar cells to ultimately recharge a battery capable of powering an ultra-low-power sensor. The fabrication process involved three main steps: first, etching wet thermal oxide materials; second, depositing metal to form contact pads; and third, transferring large-area graphene onto the chip to create the photovoltaic region. Afterward, each solar cell was placed into a housing with 28 pins, and the contact pads were wire bonded. To characterize the solar cells, we connected a DC voltage source, the solar cell, and an ammeter in series. When illuminated, with the voltage source set to zero, we measured a short-circuit current of 160 µA. As we increased the voltage, the photocurrent decreased, and at a specific voltage, it was completely suppressed, indicating the open-circuit voltage, which we found to be 0.42 V. By connecting 15 solar cells in series, we achieved a voltage output of up to 4 V, sufficient to power a 4 V system. Finally, we successfully recharged a 3 V battery using the solar cell array, closely monitoring its charging and discharging characteristics over time. This recharged battery was then used to power an ultra-low-power sensor, demonstrating the potential of graphene-based solar cells for low-power applications.