Integrated photonic crystal selective emitter for thermophotovoltaics

Abstract

Converting blackbody thermal radiation to electricity via thermophotovoltaics (TPV) is inherently inefficient. Photon recycling using cold-side filters offers potentially improved per- formance but requires extremely close spacing between the thermal emitter and the receiver, namely a high view factor. Here, we propose an alternative approach for thermal energy con- version, the use of an integrated photonic crystal selective emitter (IPSE), which combines two- dimensional photonic crystal selective emitters and filters into a single device. Finite difference time domain and current transport simulations show that IPSEs can significantly suppress sub-bandgap photons. This increases heat-to-electricity conversion for photonic crystal based emitters from 35.2 up to 41.8% at 1573 K for a GaSb photovoltaic (PV) diode with matched bandgaps of 0.7 eV. The physical basis of this enhancement is a shift from a perturbative to a nonperturbative regime, which maximized photon recycling. Furthermore, combining IPSEs with nonconductive optical waveguides eliminates a key difficulty associated with TPV: the need for precise alignment between the hot selective emitter and cool PV diode. The physical effects of both the IPSE and waveguide can be quantified in terms of an extension of the concept of an effective view factor.