Structured graphene metamaterial selective absorbers for high efficiency and omnidirectional solar thermal energy conversion

Keng-Te Lin,Baohua Jia,Tieshan Yang,Han Lin

doi:10.1038/s41467-020-15116-z

Keng-Te Lin, Baohua Jia + Show 2 more

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https://doi.org/10.1038/s41467-020-15116-z

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Abstract

An ideal solar-thermal absorber requires efficient selective absorption with a tunable bandwidth, excellent thermal conductivity and stability, and a simple structure for effective solar thermal energy conversion. Despite various solar absorbers having been demonstrated, these conditions are challenging to achieve simultaneously using conventional materials and structures. Here, we propose and demonstrate three-dimensional structured graphene metamaterial (SGM) that takes advantages of wavelength selectivity from metallic trench-like structures and broadband dispersionless nature and excellent thermal conductivity from the ultrathin graphene metamaterial film. The SGM absorbers exhibit superior solar selective and omnidirectional absorption, flexible tunability of wavelength selective absorption, excellent photothermal performance, and high thermal stability. Impressive solar-to-thermal conversion efficiency of 90.1% and solar-to-vapor efficiency of 96.2% have been achieved. These superior properties of the SGM absorber suggest it has a great potential for practical applications of solar thermal energy harvesting and manipulation.

Highlights

An ideal solar-thermal absorber requires efficient selective absorption with a tunable bandwidth, excellent thermal conductivity and stability, and a simple structure for effective solar thermal energy conversion
Many demonstrations of solar-thermal absorbers have been realized by different strategies (Supplementary Note 2), the challenges remain on the limitations of naturally available materials that can simultaneously satisfy the stringent requirements of the practical solar-thermal absorbers for high thermal conductivity, low thermal radiation loss and wavelengthselective mechanism from a simple strategy
The total solar absorbance (Eα) is not close to unity and there is no tuning mechanism presenting in this system allowing flexibly tunable absorption bandwidth to meet the requirements of efficient selective solar-thermal absorbers

Summary

Introduction

An ideal solar-thermal absorber requires efficient selective absorption with a tunable bandwidth, excellent thermal conductivity and stability, and a simple structure for effective solar thermal energy conversion. There exists a step functionlike spectral selection mechanism for the solar-thermal absorbers at a specific temperature (Supplementary Fig. 2) Such a step function has a 100% absorption overlapping as broad as possible with the solar spectrum and a 0% emission for the infrared (IR) range starting at the cut-off wavelengths, which is at the intersection of the solar spectrum (C × Esolar) and the emission spectrum (EB)[6] (Supplementary Fig. 2). From the ideal solar-thermal absorber design point of view, selective and almost total absorption across the entire solar spectrum, flexible tunability of the cut-off wavelength, and minimized excessive energy dissipation by thermal radiation in the near-IR (NIR) to mid-IR range are the essential factors. Many demonstrations of solar-thermal absorbers have been realized by different strategies (Supplementary Note 2), the challenges remain on the limitations of naturally available materials that can simultaneously satisfy the stringent requirements of the practical solar-thermal absorbers for high thermal conductivity, low thermal radiation loss (i.e., low emissivity over several tens of micrometers of wavelength in the IR regime) and wavelengthselective mechanism from a simple strategy

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