High temperature selective emitters via critical coupling of weak absorbers
Tailoring the emission spectra of a solar thermophotovoltaic emitter away from that of a blackbody, thereby minimizing transmission and thermalization loss in the energy receiver, is a viable approach to circumventing the Shockley-Queisser limit to single junction solar energy conversion. Embodiments allow for radically tuned selective thermal emission that leverages the interplay between two resonant phenomena in a simple planar structure—absorption in weakly-absorbing thin films and reflection in multi-layer dielectric stacks. A virtual screening approach is employed based on Pareto optimality to identify a small number of promising structures for a selective thermal emitter from a search space of millions, several of which approach the ideal values of a step-function selective thermal emitter.
1. A computer implemented system for identifying photonic crystals comprising:
a processor; and
a tangible computer-readable medium operatively connected to the processor and including computer code configured to:
determine emissivity for candidate emitter structures;
select an absorber to pair with the candidate emitter structures;
determine spectral conversion efficiency (η s ) and useful power (P) as figures of merit;
perform a Pareto optimization using the figures of merit; and
determine a degree of critical coupling of at least a portion of the candidate emitter structures and the selected absorber.
2. The computer implemented system of claim 1 , further comprising computer code configured to:
select an operating temperature for a photovoltaic.
3. The computer implemented system of claim 1 , wherein the figures of merit are spectral conversion efficiency (η s ) and useful power (P).
4. The computer implemented system of claim 1 , further comprising computer code configured to, prior to identifying if a parameter is Pareto optimal, determine absorption spectrum for an alloy layer of the candidate emitter structure.
5. The computer implemented system of claim 4 , further comprising computer code configured to, prior to identifying if a parameter is Pareto optimal, determine stored energy spectrum of a Bragg reflector of the candidate emitter structure.
6. The computer implemented system of claim 5 , wherein the parameters are selected from the group consisting of Bragg reflector dielectric layer thicknesses, Bragg reflector refractive indices, Bragg reflector number of such pair layers, Λ BR and the alloy layer composition, operating temperature, bandgap of an associated photovoltaic.
7. The computer implemented system of claim 5 , wherein the candidate emitter comprises a refractory metal, the Bragg reflector and the alloy layer.
8. The computer implemented system of claim 7 , wherein the refractory metal is tungsten and the alloy layer is W—Al 2 O 3 alloy.