Graphene Microflower\nby Photothermal Marangoni-Induced\nFluid Instability for Omnidirectional Broadband Photothermal Conversion

2-D\ncarbon-based materials are well-known for their broadband\nabsorption\nproperties for efficient solar energy conversion. However, their high\nreflectivity poses a challenge for achieving efficient omnidirectional\nlight absorption. Inspired by the multilevel structures of the flower,\na Graphene Microflower (GM) material with gradient refractive index\nsurface was fabricated on polymer substrates using the UV-intense\nlaser-induced phase explosion technique under the synergistic design\nof the photothermal Marangoni effect and the fluid instability principle.\nThe refractive index gradient reduces light reflection and absorbs\nat least 96% of light at incident angles of 0–60° across\nthe entire solar wavelength range (200–2500 nm). Over 90% absorption\neven at 75° angle of incidence. The light absorption is enhanced\nby the multiple interferometric phase cancelation and localized surface\nplasmon resonance, resulting in a steady-state temperature 60 °C\nhigher than ambient conditions under one solar irradiation. The max\nrate of temperature rise can reach up to 62 °C s<sup>–1</sup>. The device is then integrated at the hot end of the temperature\ndifference generator at high altitude to ensure continuous and efficient\npower generation, producing a steady-state power of 196 mW.