Broadband Epsilon-near-Zero Reflectors Enhance the Quantum Efficiency of Thin Solar Cells at Visible and Infrared Wavelengths

Abstract

The engineering of broadband absorbers to harvest white light in thin-film semiconductors is a major challenge in developing renewable materials for energy harvesting. Many solution-processed materials with high manufacturability and low cost, such as semiconductor quantum dots, require the use of film structures with thicknesses on the order of 1 μm to absorb incoming photons completely. The electron transport lengths in these media, however, are 1 order of magnitude smaller than this length, hampering further progress with this platform. Herein, we show that, by engineering suitably disordered nanoplasmonic structures, we have created a new class of dispersionless epsilon-near-zero composite materials that efficiently harness white light. Our nanostructures localize light in the dielectric region outside the epsilon-near-zero material with characteristic lengths of 10-100 nm, resulting in an efficient system for harvesting broadband light when a thin absorptive film is deposited on top of the structure. By using a combination of theory and experiments, we demonstrate that ultrathin layers down to 50 nm of colloidal quantum dots deposited atop the epsilon-near-zero material show an increase in broadband absorption ranging from 200% to 500% compared to a planar structure of the same colloidal quantum-dot-absorber average thickness. When the epsilon-near-zero nanostructures were used in an energy-harvesting module, we observed a spectrally averaged 170% broadband increase in the external quantum efficiency of the device, measured at wavelengths between 400 and 1200 nm. Atomic force microscopy and photoluminescence excitation measurements demonstrate that the properties of these epsilon-near-zero structures apply to general metals and could be used to enhance the near-field absorption of semiconductor structures more widely. We have developed an inexpensive electrochemical deposition process that enables scaled-up production of this nanomaterial for large-scale energy-harvesting applications.

Bio-inspired plasmonic leaf for enhanced light-matter interactions

“…Correspondingly, the absorption in the TE case is reduced compared with TM, as can be found in Supplementary Notes 2 the performance. Besides the photothermal experiments demonstrated here, more sophisticated applications related to energy harvesting, such as photovoltaics [33], could be realised based on the artificial leaf. The absolute absorption ability and consequently the photothermal conversion efficiency of the fractal structures may not be as good as some other Au-based absorbers [22,34], especially considering the fabrication complexity.…”

Near-Field Coupling and Mode Competition in Multiple Anapole Systems

“…We performed fully-dispersive three-dimensional FDTD simulations using our home-made simulator NANOCPP [24][25][26][27][28][29]. In our simulations, the computational domain was organized as follows: the z-aligned nanodisks were placed at the centre of a 2 µm × 2 µm × 1 µm box, with uniaxial perfectly matched layer (UPML) boundary conditions emulating an open system [30].…”

Boosting Second Harmonic Radiation from AlGaAs Nanoantennas with Epsilon-Near-Zero Materials

“…In particular, it has already been demonstrated that when an antenna is placed on top of an extremely low-permittivity substrate, the air is the "denser" medium with higher relative permittivity and therefore the antenna pattern will be predominantly backscattered into the air [20,21]. Their ability to be good reflectors and, at the same time, provide high electric field values, makes them also good candidates for energy harvesting purposes [22] and photocatalysis [23]. ENZ conditions, which occur when the real part of the dielectric permittivity crosses the zero, may be found in natural (e.g., low loss noble metals, some semiconductors and some polar dielectrics) and artificial materials (metamaterials) alike, where the latter are more flexible both in terms of the zero-crossing wavelength and effective losses [24][25][26][27].…”