Comparing the performance of thermophotovoltaic (TPV) devices is challenging due to a lack of standard operation conditions. Here, we propose a universal figure of merit (FOM) that can be used to evaluate the performance of TPV devices that operate in the far-field regime relative to their thermodynamic bounds. The introduced FOM alleviates temperature dependence and accounts for the fundamental trade-off between power density and efficiency. Based on this FOM, we present a classification of TPV performances reported in recent experiments.

Thermophotovoltaics (TPVs) differs from solar photovoltaics (PV) because pairwise efficiency and electrical power cannot be optimized simultaneously, as a consequence of spectral selectivity or photon recycling. A review of around thirty experiments conducted so far is carried out, and the achieved performances are compared with those obtained in the detailed balance limit. The link between optimal cell bandgap and emitter temperature is highlighted as a function of out-of-band radiation exchange between the emitter and the cell. The analysis reveals that almost all the experimental data reported are far from power-maximizing conditions and more focused on optimizing efficiency. At high temperature, thermal management is obviously an issue and optimizing efficiency is required to minimize heat generation. In general, it is argued that in addition to pairwise efficiency and electrical power density, heat power density is a third metric that should be considered in the design of TPV devices.

Thermophotovoltaics (TPV) is a technology that converts heat to electricity using a thermal emitter and a matched photovoltaic (PV) cell. TPV is becoming increasingly popular due to its advantages of silent power generation, higher power density (>2.5 W/cm2), reduced cost, no moving parts (thus, low maintenance costs), reaching full power in less time as compared to turbines, operating at high temperatures, and suitability for long-duration energy storage applications. This study conducts a techno-economic analysis (TEA) of a solar energy conversion (using TPV) and storage system (using phase-change materials). We optimize the levelized cost of consumed energy (LCOE) and electricity (LCOEel) using the Nelder-Mead algorithm for four scenarios (as identified in the reference study). These scenarios differ in nominal-weighted average cost of capital (WACCnom), fuel and electricity inflation rate, and capital cost factor (CAPEX) of high-temperature energy storage (HTES), power generation unit (PGU), and PV systems. We perform a sensitivity analysis that predicts a modest decrease in LCOE and LCOEel from the mean values of $0.038/kWh and $0.128/kWh, respectively. We perform a Monte Carlo uncertainty assessment and fit a probability distribution based on input variables’ historical data from the literature. The fitted probability distribution for outputs (mean, the standard deviation in brackets) is LCOE ($/kWh)—general extreme value (0.035, 0.009), and LCOEel ($/kWh)—t (0.132, 0.016). The reduced mean values for the optimized system indicate a massive potential for TPV to be economically feasible; however, the LCOEel is higher than the current average electricity price of $0.124/kWh. The box plot shows that lifetime, PV CAPEX, inflation rate, natural gas price, and WACCnom significantly impact LCOE, and future research focused on them would lead to a better adoption of TPV technology.

We present here our analysis of thin film materials crucial for the development of thermophotovoltaic (TPV) selective emitters and thermal barrier coatings (TBCs), emphasizing their high refractive index, excellent thermal stability, and transparency to infrared radiation. Utilizing spectroscopic ellipsometer measurements across the wavelength range of 210 to 2500 nm and temperatures ranging from room temperature to 1000°C, we examine the impact of temperature variations on the electronic band structures of these materials. Our study begins with the characterization of magnesium oxide and strontium titanate substrates, followed by the analysis of individual composite layers consisting of cerium oxide and barium zirconate deposited onto these substrates. Subsequently, we extend our analysis to multi-layer samples comprising combinations of these materials, aiming to project their potential performance in TPV and TBC applications.

As a method of effectively harnessing solar energy resources, the absorption efficiency of solar absorbers is of paramount importance in optimizing energy use. We propose an ultra-broadband solar absorber that utilizes a multi-resonant cavity nanopillar disc structure incorporating V2O5 and TiN. The absorption properties of the absorber are determined by the finite-difference time-domain simulation method. The results indicate an absorbance of over 90% across the entire spectral range of 300 to 2500 nm and a perfect absorption of over 99% from 540 to 2290 nm. In addition, the absorber is polarization-independent and angle-insensitive with the average absorbance above 90% even at a 60-deg incidence angle. The broadband absorption is mainly achieved by the synergistic effects of surface plasmon excitation, localized surface plasmon resonance, and multi-resonant cavity structure. The photothermal conversion efficiency of the absorber is 95.9% at 800 K. The proposed solar absorber has potential applicability in thermal photovoltaic devices and solar energy harvesting.

Smart window devices have garnered significant attention recently. Traditional thermochromic windows can control infrared (IR) radiation but not visible light, whereas liquid crystals (LCs) control visibility through voltage-controlled scattering, neglecting IR control due to forward scattering. We demonstrate that nematic LCs with a minor concentration of nanoporous microparticles (NMPs) can rapidly modulate transparency in thin devices called NMP-LCs. To concurrently control both visible and IR spectra, we propose combining a layer of ultrashort pulsed laser-patterned vanadium dioxide (VO2) with a 2% NMP composite in the LC. The patterned VO2 film serves two key functions: (i) inducing LC alignment along the nanograting lines formed by pulsed laser patterning and (ii) enabling IR radiation control with enhanced thermochromic properties compared with closed structures. The LC component facilitates visibility control via voltage or temperature modulation. The combined system thus presents a superior smart window solution, capable of efficiently managing heat and visibility with high-speed response, low voltage requirements, and minimal LC and NMP concentrations.