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Collimated thermal radiation transfer via half Maxwell's fish-eye lens for thermophotovoltaics

Journal Article · · Applied Physics Letters
DOI:https://doi.org/10.1063/1.4983679· OSTI ID:1466218
 [1];  [2];  [2]
  1. Purdue Univ., West Lafayette, IN (United States). Birck Nanotechnology Center; Purdue University
  2. Purdue Univ., West Lafayette, IN (United States). Birck Nanotechnology Center

Thermophotovoltaics (TPV) convert heat into electricity by capturing thermal radiation with a photovoltaic (PV) cell, ideally at efficiencies of 50% or more. However, excess heating of the PV cell from close proximity to the emitter substantially reduces the system efficiency. In this paper, we theoretically develop and numerically demonstrate an approach to fundamentally improving TPV systems that allow for a much greater separation of an emitter and a receiver. Thus, we solve the excess heating dilemma, required for achieving theoretically high efficiencies. It consists of a spherically graded index lens known as Maxwell's Fish-Eye (MFE) structure, capable of collimating hemispherical emission into a much narrower range of angles, close to the normal direction. To fully characterize the power radiation profile of the MFE, we perform finite-difference time-domain simulations for a quarter MFE and then map it onto a Gaussian beam approximation. The modeled beam properties are subsequently used to study a half MFE. In an optimized half MFE design, 90% of all thermal photons reach a receiver at a distance of 100 λ; by comparison, only 15.6% of a blackbody emitter reach a receiver in the same geometry. It is also shown that the emission achieved by a half MFE can lead to a photon recycling rate above 95% for below bandgap photons at an emitter-receiver separation of 100 λ. Finally, by applying a half MFE, the absolute TPV efficiency can be improved from 5.74% to 37.15%, which represents a significant step forward in realizing high-efficiency TPV systems.

Research Organization:
Purdue Univ., West Lafayette, IN (United States)
Sponsoring Organization:
USDOE Office of Energy Efficiency and Renewable Energy (EERE), Solar Energy Technologies Office (EE-4S); National Science Foundation (NSF) (United States)
Grant/Contract Number:
EE0004946
OSTI ID:
1466218
Journal Information:
Applied Physics Letters, Journal Name: Applied Physics Letters Journal Issue: 20 Vol. 110; ISSN 0003-6951
Publisher:
American Institute of Physics (AIP)Copyright Statement
Country of Publication:
United States
Language:
English

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Cited By (2)

Nanophotonic engineering of far-field thermal emitters journal May 2019
A comparatively experimental study on the temperature-dependent performance of thermophotovoltaic cells journal May 2019