TPV Devices Research Articles

Effectiveness of multi-junction cells in near-field thermophotovoltaic devices considering additional losses

Abstract Thermophotovoltaic (TPV) energy converters hold substantial potential in converting thermal radiation from high-temperature emitters into electrical energy through photovoltaic (PV) cells, offering applications ranging from solar energy harvesting to waste heat recovery. Near-field TPV (NF-TPV) devices, focused on enhancing power output density (POD), exhibit unique potential by harnessing photon tunneling. However, this potential can be mitigated by additional losses arising from high photocurrent densities and corresponding scalability issues. This study comprehensively investigates the effectiveness of multi-junction-based NF-TPV devices, accounting for additional losses. We propose two approximative expressions to quantify the impact of additional losses and characterize current density-voltage curves. Verification against rigorously optimized results establishes a criterion for effective performance. Our method provides precise POD estimations even for devices with 10 or more subcells, facilitating performance analysis across parameters like vacuum gap distance, cell width, emitter temperature, and the number of subcells compared to far-field counterparts. This research outlines a roadmap for the scalable design of NF-TPV devices, emphasizing the role of multi-junction PV cells. The analytical framework we developed will provide vital insights for future high-performance TPV devices.

A multi-junction-based near-field solar thermophotovoltaic system with a graphite intermediate structure

A solar thermophotovoltaic (STPV) system can transform incident concentrated solar energy into electrical energy with an efficiency that could be higher than the Shockley–Queisser limit. Near-field thermophotovoltaic (NF-TPV) devices can generate larger electrical power output than traditional far-field TPV devices with the aid of photon tunneling. Moreover, multi-junction PV cells can boost the performance of TPV devices by effectively distributing the absorbed photon energy inside the PV cell. In this work, we design a multi-junction-based near-field STPV system with a practical and high-temperature stable graphite intermediate structure. To optimize the system configuration, we employ a genetic algorithm and a surrogate model based on an artificial neural network, which enables us to suggest a better design approach for the multi-junction-based NF-STPV system between the power output density and power conversion efficiency maximization scenarios. When the concentration factor of the incident solar energy is 5000 and the absorber-to-emitter area ratio is 3, we can achieve a system efficiency of 23%. By introducing a material whose emissivity is as high as a blackbody on the solar absorber, the system efficiency can be further enhanced up to 35%.

Tungsten–Carbon Nanotube Composite Photonic Crystals as Thermally Stable Spectral‐Selective Absorbers and Emitters for Thermophotovoltaics

AbstractThermophotovoltaics (TPVs) is a promising energy conversion technology which can harvest wide‐spectrum thermal radiation. However, the manufacturing complexity and thermal instability of the nanophotonic absorber and emitter, which are key components of TPV devices, significantly limit their scalability and practical deployment. Here, tungsten–carbon nanotube (W‐CNT) composite photonic crystals (PhCs) exhibiting outstanding spectral and angular selectivity of photon absorbance and thermal emission are presented. The W‐CNT PhCs are fabricated by nanoscale holographic interferometry‐based patterning of a thin‐film catalyst, modulated chemical vapor deposition synthesis of high‐density CNT forest nanostructures, and infiltration of the CNT forests with tungsten via atomic layer deposition. Owing to their highly stable structure and composition, the W‐CNT PhCs exhibit negligible degradation of optical properties after annealing for 168 hours at 1273 K, which exceeds all previously reported high‐temperature PhCs. Using the measured spectral properties of the W‐CNT PhCs, the system efficiency of a GaSb‐based solar TPV (STPV) that surpasses the Shockley–Queisser efficiency limit at modest operating temperatures and input powers is numerically predicted. These findings encourage further practical development of STPVs, and this scalable fabrication method for composite nanostructures could find other applications in electromagnetic metamaterials.

Optimization of spectrally selective Si/SiO2 based filters for thermophotovoltaic devices

Design of a spectrally selective filter based on one-dimensional Si/SiO2 layers is considered for improved performance of thermo-photovoltaic devices. Spectrally selective filters transmit only the convertible radiation from the emitter as non-convertible radiation leads to a reduction in cell efficiency due to heating. The presented Si/SiO2 based filter concept reflects the major part of the undesired range back to the emitter to minimize energy required for the process and it is adaptable to different types of cells and emitters with different temperatures since its cut-off wavelength can be tuned. While this study mainly focuses on InGaSb based thermo-photovoltaic cell, Si, GaSb, and Ga0.78In0.22As0.19Sb0.81 based cells are also examined. Transmittance of the structure is predicted by rigorous coupled wave approach. Genetic algorithm, which is a global optimization method, is used to find the best possible filter structure by considering the overall efficiency as an objective function that is maximized. The simulations show that significant enhancement in the overall system and device efficiency is possible by using such filters with TPV devices. The methodology described in this paper allows for an improved filter design procedure for selected applications.

MOCVD growth and properties of Zn3P2 and Cd3P2 films for thermal photovoltaic applications

We report the growth and characterization (structural and electronic) of thin films of Zn3P2 and Cd3P2 grown by MOCVD. Heterojunctions of this pair of dopable semiconductors are being studied for applications as thermophotovoltaic devices. We have grown films of these materials on glass substrates, and X-ray diffaction studies confirm the phase formation and polycrystalline nature of the films. Optical absorption studies revealed three distinct transitions in the Zn3P2 films, at 1.3, 1.55, and 1.85 eV (in agreement with literature values found in single crystals). Analysis of optical spectra of the films showed direct transitions at 0.62, 0.65, and 0.71 eV. We also report measurements of photoconductivity and photoluminescence in these films. Hall effect measurements show the Cd3P2 films to be n-type with mobilities as high as 429 cm2/V s. Carrier lifetimes were also measured directly by a photoconductive decay technique. The films show promise for TPV devices, although fabrication of such multilayer devices is in only a preliminary stage.

Liquid-phase epitaxy of low-bandgap III–V antimonides for thermophotovoltaic devices

Liquid-phase epitaxial (LPE) growth of low-bandgap III–V antimonides is developed for thermophotovoltaic and other optoelectronic device applications. Epitaxial layers of AlGaAsSb, InGaAsSb, and InAsSbP, with thicknesses up to 200 μm, can be grown in a single LPE step. TPV devices based on InAsSbP extend the spectral response to a wavelength of 3500 nm. These single-epilayer structures are compatible with post-growth zinc diffusion processes that produce high-performance TPV devices. Thick epitaxial layers are also conducive for epilayer film transfer to surrogate substrates and subsequent removal of the GaSb and InAs seeding substrate. An insulating surrogate substrate facilitates isolation schemes for monolithic series-interconnected TPV arrays, and a reflective substrate acting as a backside mirror is used to effect photon recycling.