Metamaterial Absorber for Solar Thermophotovoltaic Systems

Abstract

Utilizing solar energy for various purposes like generating electricity or for heating purpose requires efficient absorption of solar energy. This can be done by using current state of the art ultrathin metasurface based solar absorbers. The STPV system is a kind of heat engine that absorbs broadband solar spectrum and emits a narrow band spectrum required for solar cells to generate electrical power. After the absorber absorbs broadband solar radiations, the emitter part of STPV emits a narrow sub-spectrum band, which is spectrally matched with the bandgap of respective solar cell, to obtain maximum efficiency for the solar cell. However, the efficiency of overall STPV system is directly dependent upon the efficiency of the absorber and emitter; therefore, the absorber should absorb the solar spectrum efficiently. Moreover, the elements of STPV system i.e. absorber and emitter, must withstand high temperatures without reducing the efficiency or getting self-damaged. This paper presents Titanium Carbide (TiC has a high melting point of 3067°C) based pyramid-shaped solar absorber, which has perfect absorptance for the visible regime and absorbs a significant spectrum of IR radiations till 2000nm. The proposed solar absorber has an efficiency of 88% (i.e. captures 88% of total energy emitted from a blackbody) for broadband solar spectrum from 400nm to 2000nm range where most of the solar energy lies. The proposed design has an average absorptance greater than 99% for the 400-800nm visible range and 73% for 400-2000nm. High absorptance is due to the magnetic resonance which causes impedance matching with free space. The proposed design is ultrathin, having a thickness of 306nm only, and implements MIM (Metal-Insulator-Metal) configuration. These types of absorbers have wide applications in optical sensing, integrated photonics, thermal imaging, color imaging, and electromagnetic shielding. Other valuable applications include polarizers, modulators, and cloaking. They are also used in heating elements such as solar geysers and solar furnaces.