Thermodynamic performance bounds for radiative heat engines

This paper discusses the performance limits of heat engines exchanging heat radiatively with a hot source while in thermal contact with a cold sink. Starting from solar energy conversion models, we derive power-versus-efficiency upper bounds for both reciprocal and nonreciprocal radiative heat engines. We find that nonreciprocal engines may allow significantly better performance than reciprocal ones, particularly for low emitter temperatures or when operating close to Carnot efficiency. The results give valuable guidelines for the design and optimization of thermophotovoltaic systems.Comment: 6 pages, 5 figure

Design of narrowband infrared emitters by hybridizing guided-mode resonance structures with van der Waals materials

In this paper, narrowband emitters have been designed using particle swarm optimization (PSO) in the 10-20 {\mu}m infrared range. The device structure consists of an anisotropic {\alpha}-MoO3 layer combined with the one- and two-dimensional guided-mode resonance structures. Well-defined absorption lines are present in the reflection spectrum for both TE and TM polarizations, thereby yielding narrowband emissivity at desired wavelengths. The band structure of the designed emitters under TM polarization demonstrates distinct features unlike its TE counterpart. These features are attributed to the interaction between guided-mode resonances and phonon polaritons. The results are relevant for applications in active and passive photonic elements in mid- and long-wave IR bands

Design rules for active control of narrowband thermal emission using phase-change materials

We propose an analytical framework to design actively tunable narrowband thermal emitters at infrared frequencies. We exemplify the proposed design rules using phase-change materials (PCM), considering dielectric-to-dielectric PCMs (e.g. GSST) and dielectric-to-metal PCMs (e.g. $\mathrm{VO_2}$). Based on these, we numerically illustrate near-unity ON-OFF switching and arbitrarily large spectral shifting between two emission wavelengths, respectively. The proposed systems are lithography-free and consist of one or several thin emitter layers, a spacer layer which includes the PCM, and a back reflector. Our model applies to normal incidence, though we show that the behavior is essentially angle-independent. The presented formalism is general and can be extended to \textit{any} mechanism that modifies the optical properties of a material, such as electrostatic gating or thermo-optical modulation.Comment: 9 pages, 6 figure

Deep-subwavelength Phase Retarders at Mid-Infrared Frequencies with van der Waals Flakes

Phase retardation is a cornerstone of modern optics, yet, at mid-infrared (mid-IR) frequencies, it remains a major challenge due to the scarcity of simultaneously transparent and birefringent crystals. Most materials resonantly absorb due to lattice vibrations occurring at mid-IR frequencies, and natural birefringence is weak, calling for hundreds of microns to millimeters-thick phase retarders for sufficient polarization rotation. We demonstrate mid-IR phase retardation with flakes of $\alpha$-molybdenum trioxide ($\alpha$-MoO$_3$) that are more than ten times thinner than the operational wavelength, achieving 90 degrees polarization rotation within one micrometer of material. We report conversion ratios above 50% in reflection and transmission mode, and wavelength tunability by several micrometers. Our results showcase that exfoliated flakes of low-dimensional crystals can serve as a platform for mid-IR miniaturized integrated polarization control.Comment: 8 pages, 5 figure

Optical simulations and optimization of perovskite/CI(G)S tandem solar cells using the transfer matrix method

In this work we employ the transfer matrix method for the analysis of optical materials properties to simulate and optimize monolithic tandem solar cell devices based on CuIn$_{1−x}$Ga$_x$Se$_2$, CI(G)S, and perovskite (PVK) absorbers. By finding models that fit well the experimental data of the CI(G)S solar cell, the semitransparent perovskite solar cell (PSC) and the PVK/CI(G)S monolithic tandem solar cell, we were able to perform a detailed optical loss analysis that allowed us to determine sources of parasitic absorption. We found better substitute materials for the transport layers to increase the power conversion efficiency and, in case of semitransparent PSCs, sub-bandgap transmittance. Our results set guidelines for the monolithic PVK/CI(G)S tandem solar cells development, predicting an achievable efficiency of 30%

New limits for light-trapping with multi-resonant absorption

International audienc

Solar cells combining hot carriers and multijunctions: synergies and insights from Maxime Giteau, Samy Almosni, and Daniel Suchet

International audienc

Resonant absorption in multilayer quantum-well and quantum-dot solar cells

Epitaxially-grown quantum well and quantum dot solar cells suffer from weak light absorption, strongly limiting their performance. Light trapping based on optical resonances is particularly relevant for such devices to increase light absorption and thereby current generation. Compared to homogeneous media, the position of the quantum layers within the device is an additional parameter that can strongly influence resonant absorption. However, this effect has so far received little attention from the photovoltaic community. In this work, we develop a theoretical framework to evaluate and optimize resonant light absorption in a thin slab with multiple quantum layers. Using numerical simulations, we show that the position of the layers can make the difference between strong absorption enhancement and completely suppressed absorption, and that an optimal position leads to an absorption enhancement twice larger than average. We confirm these results experimentally by measuring the absorption enhancement from photoluminescence spectra in InAs/GaAs quantum dot samples. Overall, this work provides an additional degree of freedom to substantially improve absorption, encouraging the development of quantum wells and quantum dots-based devices such as intermediate-band solar cells.Comment: 29 pages, 6 figure

Hot-carrier multi-junction solar cells: A synergistic approach

International audienceConventional single-junction solar cells have a theoretical efficiency limit around 33%, and multi-junction solar cells (MJSCs) are currently the only technology to overcome this limit. The demonstration of hot-carrier solar cells (HCSCs), another high-efficiency approach that relies on harvesting the kinetic energy of the photo-generated carriers, has so far been hindered due to the difficulty of mitigating carriers' thermalization. In this letter, we highlight the synergies of these two concepts by introducing the hot-carrier multi-junction solar cell (HCMJSC), a MJSC with a thin hot-carrier top junction. Using a detailed balance model, we compare the efficiency of different devices as a function of three parameters: the bandgap of the top and bottom junctions, the top cell thickness, and an effective thermalization coefficient, which encapsulates information on both thermalization and light trapping. Besides allowing for a much broader range of material combinations than MJSCs, we show that HCMJSCs can reach efficiencies higher than MJSCs with a larger thermalization coefficient than HCSCs. As such, HCMJSCs could provide a preferred route toward the development of hot-carrier-based high efficiency devices