<p>The growing demand for high-power and energy-dense storage devices necessitates the development of advanced supercapacitor systems that can directly integrate with renewable energy sources. Here, we report an ionic liquid-driven supercapacitor (IL-SSC) device employing defect-engineered few-layer graphene (F-Gr) electrodes using tetraethylammonium tetrafluoroborate (TEABF₄) in acetonitrile electrolyte. F-Gr, prepared via a double-step reduction and thermal activation strategy, exhibits ideal interlayer spacing, less oxygen groups, and restored sp² networks, enabling rapid ion transport and superior conductivity. Structural and spectroscopic analyses confirm effective deoxygenation and defect tailoring, while density functional theory calculations reveal enhanced electronic delocalization of F-Gr compared to rGO. Electrochemically, the F-Gr device sustains an extended operating voltage of 3.0&#xa0;V, delivering a high specific capacitance of 50&#xa0;F g^− 1 @ 10 mV s^− 1, and an energy density of 50.7 Wh kg^− 1 (@ 1.25&#xa0;A g^− 1), with a peak power density of 18,750&#xa0;W kg^− 1 (@ 12.5&#xa0;A g^− 1), with 85% capacitance retention after 5000 cycles. The F-Gr IL-SCC device maintains stable performance across a wide temperature window (-10 to 80&#xa0;°C), highlighting robust ion dynamics in extreme sub-zero and high-temperature resilient conditions. Furthermore, direct integration with a photovoltaic panel demonstrates rapid solar charging to ~ 3&#xa0;V within 20&#xa0;s and successful powering of a portable electronic load. Establishing the F-Gr IL-SSC device as a versatile platform bridging the gap between batteries and capacitors, offering a promising route toward high-performance, renewable energy storage and off-grid applications.</p> Graphical abstract <p></p>