Systematic Analyses of the Ideal Selective Spectrum and the Practical Design Strategies for the Solar Thermophotovoltaic System

Solar thermophotovoltaic (STPV) systems can break the Shockley–Queisser (SQ) limit through selective absorbers and emitters, whose ideal emissivity is crucial as a design target. In this paper, we systematically analyze the ideal selective spectrum and solve the conflict between energy and efficiency in photothermal conversion efficiency by modifying the corresponding equation. The ideal emissivity of the absorber is one in [Ec, ∞] and zero out of this range. For actual design, if spectra deviation cannot be avoided, Ec is preferable to redshifting. The ideal emissivity of the emitter is one in [Eg,Emax] and the decrease in Emin should be suppressed relative to Emax. Besides, the optimal bandwidth of the emitter is about 0.08 eV for different photovoltaic cells and working conditions, which gives a rough and valuable guide in practical design. The analytical progress and design strategies will give a reference and direction for the future design of STPV.