An Ultrathin, Nanogradient, and Substrate-Independent WOx-Based Film as a High Performance Flexible Solar Absorber

Advances in flexible and wearable energy-related devices increase the need for highly efficient, low-cost, ultrathin solar selective absorber coatings (SSACs). Herein, the fabrication of nanogradient WOx-based SSACs with excellent properties, including a superior solar absorptance of 0.93, an outstanding thermal robustness of up to 300 degrees C, and substrate independence, is reported. More importantly, the thickness of WOx-based SSACs is only approximately 100 nm, which is substantially thinner than all other reported SSACs. These features arise from the two intrinsically absorptive WOx layers on a thin nanoplasmonic W layer. The deposition process is based on self-doped reactive sputtering via limited tungsten oxidation due to a small amount of oxygen. The WOx-based SSACs on a flexible polyimide sheet demonstrate stable performance, strong adhesion, and bendable nature. The proposed self-doped fabrication process provides a new way to design cost-effective ultrathin SSACs to meet the demand for large-scale flexible energy harvesting and supply applications.