Session M64: Optoelectronic and Photovoltaic Energy Conversion

Near field heat transfer and related phenomena in 2D materials

Thermal quantum fluctuations of transient current densities result in electromagnetic fluctuations giving rise to several fundamental phenomena, such as near-field radiation, Casimir pressure, and quantum friction. Using the cross-spectral density of electric fields within a Green’s function formalism, we derive expressions for the near field transfer coefficient, Casimir force, and quantum friction force for 2D systems described by the most general optical response that takes into account optical anisotropy and Hall response of the materials. This framework is then used to set the stage for calculating the near field transfer with optical response properties obtained from first principles simulations. We then target different classes of 2D systems, such as transition metal dichalcogenides, to establish emerging trends of electronic, structural, and optical properties as means to control and manipulate near-field transfer in real materials.   

Correlating Photoluminescence with Total Volume in Suspended Binary Superlattices of Infrared Colloidal Nanocrystals Using Transmission Electron Microscopy

By combining infrared semiconductor colloidal nanocrystals (NCs) into three-dimensional superlattices, new optoelectronic properties become available and are controllable through careful choice of the constituent nanocrystals and their chemical interactions. Here, we fabricate large (>1 μm) domains of binary nanocrystal superlattices made up of infrared plasmonic Cu_2-xS/PbS core/shell and excitonic PbS nanocrystals, which are suspended over holes for further transmission electron microscopy and optical characterization.  We determine both thickness and spatial extent of the superlattice to define the local volume in individual superlattice domains, which directly correlates to photoluminescence. Combined with time-resolved photoluminescence spectroscopy, these results indicate that energy transfer occurs between the excitonic emitters and plasmonic nanocrystals, which we will discuss in context with computational investigations.   

Accelerated Screening of Ternary Chalcogenides for Multifunctional Energy Applications

Chalcogenides have attracted considerable attention in multiple fields of applications, such as optoelectronics, thermoelectrics, transparent contacts, and thin-film transistors. However, the number of synthesized chalcogenides remains relatively low compared to that of oxides. In this study, we performed systematic high-throughput screening combining first-principles calculations and machine learning modeling to identify novel ternary chalcogenides for energy applications. More than 400,000 compounds are considered by exploiting the ion-substitution approach for the 32 most frequent crystal structure prototypes in the database, with their thermodynamic stabilities evaluated by collecting all available binary and ternary chalcogenides from the OQMD database. This gives rise to a comprehensive database, enabling us to quantify the structural maps and model the thermodynamic stabilities via machine learning. In addition, to guide further experimental synthesis, we modeled the synthesizability of such ternary chalcogenides using the CGCNN approach, giving rise to a series of candidates with a high likelihood of being synthesized experimentally. Furthermore, the functional properties of the (meta-)stable compounds were investigated following the magnitude of the band gaps, obtained via self-consistent hybrid functional calculations. Correspondingly, we performed further calculations to identify for potential candidates for photovoltaic and thermoelectric applications, with the properly formulated characteristic figure of merits and implemented computational workflows. Last but not least, machine learning modeling of such physical properties was carried out based on Bayesian optimization, and we demonstrated how to explore such a large chemical space to obtain materials with optimal physical properties, enabling us to perform inverse design of functional chalcogenides in the future.   

Designing AM2Pn2 Materials for Use as Solar Photovoltaics by Alloying

Some compositions of the formula AM₂Pn₂ have recently been observed as promising solar absorbers through high-throughput computing. In this talk, I will discuss generating new candidate materials from a parent structure by isovalent substitutions (A= Ba, Sr, Ca, Yb, Eu, Mg, M=Mn, Mg, Cd, Zn, Pn= Bi, Sb, As, P). We explore the thermodynamic and electronic properties of these compounds to screen for those which may be high efficiency solar photovoltaics. We find that in this family many of the materials are thermodynamically stable in the same crystal structure and have a range of computed bandgaps. In order to further increase the design space for an optimal material, the alloys between the endmember AM₂Pn₂ compounds will be considered for their effect on stability and optical properties. I will discuss computational tools to screen for stable and desirable alloys in a high throughput fashion and suggest guidelines for materials that may be promising for use as single junction or tandem solar cells.   

The defect chemistry of emerging, wide-bandgap absorber BiOI

Wide bandgap solar absorbers are seeing significant interest for a variety emerging photovoltaic technologies, from top-layers in tandem cells to single junction devices for indoor applications. V-VI-VII materials have been studied for photocatalysis, but have recently gained interest as “perovskite-inspired” materials (PIMs) for solar absorber applications.^[1] These are materials which stray from the perovskite structure, but share an elemental space, thus keeping the strong antibonding character at the band edges and large dielectric constant, which are associated with the defect tolerance observed in lead halide perovskites.   

 

From the family of bismuth-based absorbers, BiOI has emerged as a leading candidate due to its improved air stability and lack of ultrafast charge-carrier localization, which can pose a challenge for many Bi containing PIMs originating from the reduction in dimensionality.^[1,2,3] However, large concentrations of electron traps have been measured in BiOI thin films, the potential source of poor device performance.^[4]  

 

Therefore, in this project we perform the first, complete investigation into all intrinsic point defect in BiOI at the hybrid DFT level, using the ShakenBreak method to thoroughly search the complex defect potential energy surface.^[5] This will allow the identification of harmful defects and guide the development of fabrication processes to reduce their impact.  

 

 

[1] Y.-T. Huang, S. R. Kavanagh, D. O. Scanlon, A. Walsh, R. L. Z. Hoye, Nanotechnology, 2021, 32, 132004. 

[2] D. S. Bhachu, S. J. A. Moniz, S. Sathasivam, D. O. Scanlon, A. Walsh, S. M. Bawaked, M. Mokhtar, A. Y. Obaid, I. P. Parkin, J. Tang and C. J. Carmalt, Chem. Sci., 2016, 7, 4832 

[3] A. M. Ganose, M. Cuff, K. T. Butler, A. Walsh, D. O. Scanlon, Chem. Mater., 2016, 28, 1980 

[4] S. Lal, M. Righetto, A. M. Ulatowski, S. G. Motti, Z. Sun, J. L. MacManus-Driscoll, R. L. Z. Hoye, L. M. Herz, J. Phys. Chem. Lett., 2023, 14, 6620–6629 

[5] I. Mosquera-Lois, S. R. Kavanagh, D. O. Scanlon, A. Walsh, npj Comput. Mater., 2023, 9, 1 —11    

Virtual substrates for wide bandgap AlyX1-yN growth

Lattice-matched substrates are critical for growth of high quality, compositionally-targeted ternary Al_yX_1-yN compounds with properties suitable for a wide variety of next-generation opto- and power electronic applications. [DOI:10.1149/2.0111702jss] We have identified the (111) plane of transition metal carbides and nitrides as lattice matched “virtual” substrate layers that have additional benefits of electrical conductivity and appropriate coefficients of thermal expansion for nitride layer at both growth and operating temperatures. [arXiv:2208.11769 2022]

 

In this work, (111)-oriented TaC and ZrN are grown by RF sputtering and optimized as substrate layers for Al_yGa_1-yN and Al_yGd_1-yN, respectively. TaC is demonstrated as a full proof of concept. (111)-stabilized TaC layers with a rock-salt crystal structure are annealed to improve surface crystal quality and surface morphology and then used as a template for growth of an Al_0.7Ga_0.3N layer by molecular beam epitaxy. X-ray diffraction (XRD) demonstrates epitaxial registry of the grown layer to the substrate. High resolution transmission electron microscopy (TEM) is used to investigate interface behavior, showing regions of abrupt interface transitions and nitrogen polar termination of the Al_0.7Ga_0.3N. We also grew (111)-oriented ZrN on Ti-Zr-N graded buffer layers as a lattice-matched virtual substrate for Al_yGd_1-yN. Structure, morphology, and strain are analyzed using XRD and atomic force microscopy. Structure and quality of initial Al_0.8Gd_0.2N thin films are investigated for both in-situ and ex-situ growths.   

Flexible Nanocomposite Materials for Energy Harvesting and Heat Management

Today's quest for sustainable energy solutions through greener energy harvesting and heat-management technologies has recently developed a significant interest in new flexible and biocompatible nanocomposite ceramics with large electromechanical, triboelectric, and electrocaloric (EC) effects [1]. Therefore, an overview of experimental and theoretical investigations of the large EC, piezoelectric, and triboelectric response in flexible ceramic nanocomposites exploiting enhanced multiferroic properties of ferroelectric nanoparticles within the polymer matrix will be presented in this contribution. Specifically, the enhanced EC response in thin PMN-PT films and in lead-free BCZT and BaTiO3-based nanoparticles will be reviewed, including flexible polymer composites' large energy harvesting potential [2]. The impact of filler's dielectric permittivity and aspect ratio in high-k polymer and the benefits of combining 1D and 3D nanofillers on enhanced properties of flexible nanocomposites will be discussed [3]. [1] Z. Kutnjak., B. Rožič, R. Pirc., Wiley Encyclopedia of Electrical and Electronics Engineering, 1-19 (2015). [2] Z. Hanani et al., Nano Energy 81, 105661 (2021). [3] Z. Hanani et al., Nanoscale Adv. 4, 4658 (2022).   

Unitary control of optical absorption and emission

Thermal radiation is a pervasive phenomenon, with significant implications in renewable energy, imaging, and sensing technologies. Unitary control changes the absorption and emission of an object by transforming the external light modes that the photonic structures interact with. It is widely used in applications and underlies coherent perfect absorption. However, two basic questions remain unanswered: (i) Given a specific object, what are the achievable absorptivity, emissivity, and nonreciprocal contrast for each mode under unitary control? (ii) How can the desired absorptivity, emissivity, or nonreciprocal contrast for each mode be obtained through unitary control? The first question seeks to understand the capabilities and limitations of unitary control, while the second question focuses on practical implementation. Here, we provide a complete solution to both questions using the mathematical theory of majorization. We demonstrate that unitary control can achieve perfect violation or preservation of Kirchhoff's law in nonreciprocal objects, as well as uniform absorption or emission for any object.   

Measurement of broadband nonreciprocal thermal radiation

Until recently, differences in the spectral directional emissivity and absorptivity have been either narrowband [1] or shown at wavelengths well beyond the infrared regime [2]. We report nonreciprocal, broadband (12.5 mm – 16 mm) thermal radiation from gradient epsilon-near-zero (ENZ), degenerately-doped (n = 1.5 – 4.5 x 10¹⁸ cm^-3) InAs layers of subwavelength thicknesses (50 nm and 150 nm) that support a broadband Berreman mode. We measure both the spectral directional absorptivity and emissivity of the structure when a moderate transverse magnetic field (1 T) is applied and observe an opposite magnetic-field-dependent tuning of the two values across a wide angular range (5° < q < 75°). The broadband and nonreciprocal effect both rely on the ENZ condition of the individual InAs layers, meaning that the spectral window of the nonreciprocal radiation is tunable by the carrier concentrations of the InAs layers. The directionality of the emitted broadband radiation is determined by the thicknesses of the constituent layers. Using an angle-resolved thermal emission spectroscopy (ARTES) setup, we are able to experimentally compare the directional dependence of the magnetic field effect on the emissivity for varying thickness samples.

 

[1] K. J. Shayegan, S. Biswas, B. Zhao, S. Fan, and H. A. Atwater, “Direct observation of the violation of Kirchhoff’s law of thermal radiation,” Nat. Photon. (s41566-023-01261-6), 1-16 (2023).

[2] Y. Hadad, J. C. Soric, and A. Alu, “Breaking temporal symmetries for emission and absorption,” PNAS 113(13), 3471-3475 (2016).   

Thermal Analysis of a Solar Light Trapping Particle Receiver using Computational Fluid Dynamics

Light-trapping particle receivers are a promising choice for 3rd-generation concentrating solar power (CSP) systems. Achieving thermal efficiencies exceeding 90% is imperative for the competitiveness of CSP systems compared to non-renewable fuels. It is equally critical to maintain peak panel temperatures below 900^oC to ensure material integrity. This study conducts a comprehensive analysis of light-trapping receiver panels at an integrated system level, aiming to understand the heat transfer physics associated with free convection and radiation from panel surfaces. ANSYS Fluent is employed as a Computational Fluid Dynamics (CFD) tool, for this purpose. The ANSYS CFD model incorporates incident solar flux on the receiver panels and the heat flux absorbed through falling particles behind these panels, enabling the prediction of the resulting temperature profiles. Subsequent to post-processing the flux integrals across the panel surfaces, the study characterizes thermal efficiency of receiver panels. Additionally, the research explores the sensitivity of thermal efficiency to key system parameters, including the particle heat transfer coefficient, particle inlet temperature, and flux intensity. To further enhance efficiency, a concept involving a protective heat shield is proposed and computationally tested to establish its viability. The study also generates 3D temperature profiles, which will assist in future thermo-mechanical analyses of these receiver panels.