Mirror-backed Dark Alumina: A Nearly Perfect Absorber for Thermoelectronics and Thermophotovotaics.

Mohamed Farhat,Hakan Bağcı,Mark Ming-Cheng Cheng,Khai Q Le,Tsung-Chieh Cheng,Pai-Yen Chen

doi:10.1038/srep19984

Abstract

We present here a broadband, wide-angle, and polarization-independent nearly perfect absorber consisting of mirror-backed nanoporous alumina. By electrochemically anodizing the disordered multicomponent aluminum and properly tailoring the thickness and air-filling fraction of nanoporous alumina, according to the Maxwell-Garnet mixture theory, a large-area dark alumina can be made with excellent photothermal properties and absorption larger than 93% over a wide wavelength range spanning from near-infrared to ultraviolet light, i.e. 250 nm–2500 nm. The measured absorption is orders of magnitude greater than other reported anodized porous alumina, typically semi-transparent at similar wavelengths. This simple yet effective approach, however, does not require any lithography, nano-mixture deposition, pre- and post-treatment. Here, we also envisage and theoretically investigate the practical use of proposed absorbers and/or photothermal converters in integrated thermoelectronic and/or thermophotovoltaic energy conversion devices, which make efficient use of the entire spectrum of ambient visible to near-infrared radiation.

Highlights

A 2cm× 2cm commercial 6061-T6 aluminum alloy was treated by a standard electrolytic polishing
The nanoporous alumina made from impurity-rich aluminum via the electrochemical anodization can be optically lossy, while having a real-valued optical impedance matched to that of the free space
The photothermal experiment further demonstrates the viability of proposed absorber in practical energy conversion applications

Summary

Introduction

With the rapid advent of nanotechnology, design of highly-efficient and compact antireflection coatings or surface absorbers has become viable using nanophotonic techniques: photonic nanostructures[18,19,20,21,22,23,24,25,26,27,28,29], photonic crystals[30,31], and metamaterials[15,16,17]. Aiming to facilitate the use of TC and TPV energy conversion devices, here we develop a simple and cost-effective chemical route to prepare a high-performance, large-area absorber constructed using a nanoporous alumina film on top of the commercial 6061-T6 aluminum (Al) substrate.

Results

Conclusion