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

Abstract

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 WO x -based SSACs with excellent properties, including a superior solar absorptance of 0.93, an outstanding thermal robustness of up to 300 C, and substrate independence, is reported. More importantly, the thickness of WO x -based SSACs is only approximately 100 nm, which is substantially thinner than all other reported SSACs. These features arise from the two intrinsically absorptive WO x 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 WO x -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.

Spectral properties and microstructure of sputtered WOx films for solar conversion applications

“…The SSACs on Cu substrate showed a poor α of 0.88 and ε of 0.062. Such result was different from the traditional four‐layer double‐cermet SSACs, such as W‐Al 2 O 3 , Mo‐SiO 2 , Al‐AlN, and CrAlSiN . Compared with the recently reported multilayer absorbers (Table ), the WO x /SiO 2 SSACs showed similar optical performance, whereas the SSACs presented a simple structure and low process cost.…”

Solar Selective Absorber for Emerging Sustainable Applications

“…Wang's group used self-doped single target magnetron sputtering technology to prepare a series of ultrathin SSACs that can be deposited on flexible substrates. For example, a SSAC based on WO x with a nanogradient that is only about 100 nm thick has a high solar absorption of 0.93 and excellent thermal stability at 300 C. [143] A SSAC based on MoO x with a nanogradient, when SSAC is coated on fabric and polymer, under 1 sun irradiation, the surface temperature reaches 90 C and 78 C, respectively, which realizes efficient photothermal conversion due to the excellent absorption of SSAC. [144] A SSAC of amorphous carbon doped by Ag NPs with a thickness of only 130 nm, it can achieve 87% photothermal conversion efficiency due to a significant enhancement of light absorption by the plasmonic effect of Ag NPs.…”

Spectrally Selective Absorbers/Emitters for Solar Steam Generation and Radiative Cooling‐Enabled Atmospheric Water Harvesting

“…High‐performance cermet SSAs generally have two or more layers of cermet with gradient metal fraction that are fabricated by co‐sputtering methods, accompanied by a bottom IR reflector and top antireflection layers ( Figure a). [ 30,127,128 ] The gradient metal fraction leads to the gradient refractive index from the bottom to top, and therefore minimized surface reflection. W is the most frequently used metal in cermets because of its high optical loss and high‐temperature reliability.…”

“…W is the most frequently used metal in cermets because of its high optical loss and high‐temperature reliability. [ 128–135 ] In 2015, Cao et al. demonstrated a multilayer cermet of W and Ni nanoparticles and a Al 2 O 3 host by a co‐sputtering method, showing a high of 90% and a low of 15% at 500 °C, as well as thermal stability at 600 °C (Figure 11b).…”