Solar radiation is the Earth's most plentiful renewable energy source. Metasurface-based nanostructures can store solar energy efficiently and exhibit consistent behavior when interacting with light waves. This study investigates an ultra-thin, ultra-wideband solar absorber and thermal emitter that operates in the 400-5000 nm spectrum. The proposed structure design consists of a thin MXene monolayer at the top, followed by a nickel-made fractal L-shaped resonator film mounted on a SiO2 substrate. This device achieves greater than 90% of the aggregative absorption over the 4133 nm ultra-wideband region ranging from 867 nm to 5000 nm. Within its operational band, the solar absorber exhibits excellent solar energy storage capabilities under the solar AM 1.5 model curve. Furthermore, the absorber structure maintains a stable thermal radiation efficiency of 94.5-95.5% over the temperature range of 300-700 K. In addition, the physical mechanism underlying the device's ultra-wideband high absorption characteristics is adequately explained using impedance matching theory and the distribution of surface current density at high absorption wavelengths. The proposed structure design's symmetry shows excellent resilience to polarization state variations as well as wide angular stability to maintain high absorption rate. Given all of these advantages, the proposed structure would be highly suitable for solar energy and thermal radiation applications.