Journal Articles
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Item Asymmetric Thermoelectric Performance Tuning in Low-Cost ZrFexNi1-xSb Double Half-Heusler Materials(American Chemical Society, 2023) Kahiu, J.N.; Kihoi, S.K.; Kim, H.; Shenoy, U.S.; Bhat, D.K.; Lee, H.S.The new paradigm for increasing the commercial viability of thermoelectric materials in the energy sector is the theoretical prediction and subsequent experimental validation and optimization of cheaper and inherently more efficient compositions. Herein, the experimental validation of the recently theoretically predicted ZrFe0.50Ni0.50Sb double half-Heusler and the ability to intrinsically tune this system to optimized p- or n-type materials by varying the Fe/Ni ratio in the synthesized ZrFexNi1-xSb (x = 0.35-0.65) samples are demonstrated. The samples are synthesized by arc melting, hot pressing, and annealing. Subsequent microstructural analysis confirms the crystallization of the ZrFexNi1-xSb into the half-Heusler structure and reveals that the variation of the Fe/Ni ratio favors the Ni-rich side. Consequently, the best p-type x = 0.55 and n-type x = 0.35 samples exhibit higher power factor values stemming from an increased carrier concentration, higher density of state effective mass, and suppressed bipolar conduction, as indicated by the Hall data analysis and density functional theory simulations. The additional lattice disorders introduced by varying the Fe/Ni ratio suppress the thermal conductivity and increase the microhardness of the n-type samples. The ZrFe0.35Ni0.65Sb and ZrFe0.55Ni0.45Sb samples achieve maximum zTs of ∼0.43 and 0.06, respectively, which is a great improvement over the ∼0.001 value of the ZrFe0.50Ni0.50Sb sample. These results highlight the viability of tuning the performance of double half-Heuslers on the doubly doped site. They will be instrumental in demonstrating the feasibility of developing low-cost double half-Heusler materials with better intrinsic and highly tunable properties. © 2023 American Chemical Society.Item Tailoring the Thermoelectric Performance of the Layered Topological Insulator SnSb2Te4 through Bi Positional Doping at the Sn and Sb Cation Sites(American Chemical Society, 2023) Kihoi, S.K.; Shenoy, U.S.; Kahiu, J.N.; Kim, H.; Bhat, D.K.; Lee, H.S.Ongoing research and development focus on emerging thermoelectric materials with enhanced performance, continually making the possibility of waste heat recovery a reality. In this work, we engineer the thermoelectric properties of the layered SnSb2Te4 topological insulators. To date, there is little research reporting on these materials as potential state-of-the-art thermoelectric materials. Thus, there is a need to formulate effective strategies to realize this potential. Since these materials are known to have intrinsically low lattice thermal conductivity, we shift our attention to improving the electrical transport properties. For the first time, positional Bi doping at both the Sn and Sb cation sites is adopted. The aliovalent and isovalent nature of Bi at these sites, respectively, is shown to cause significant improvements in the performance of these layered materials. The electronic band structure of the pure and doped samples, where we considered various occupancies, is studied whereby we reveal the occurrence of band convergence and resonant levels resulting in a high power factor of ∼10.8 μW cm-1 K-2 at 623 K. Overall, a high ZT of ∼0.46 at a relatively lower temperature of 673 K is recorded. The potential of these materials for thermoelectric applications is shown, especially in the case of Bi doping at the Sn cation site. Continued efforts to enhance the thermoelectric performance of these topological insulators are needed for them to gain a substantial competitive edge in comparison to other state-of-the-art thermoelectric materials. © 2023 American Chemical Society.Item DFT Study about the Effect of Doping on the Properties of GaSb Material and Designing of High-Efficiency Infrared Photodetector(John Wiley and Sons Inc, 2023) Bhandari, B.; Yadav, A.K.; Singh, R.; Kiran, G.; Singh, A.K.; Garg, V.; Pandey, S.K.The gallium antimonide (GaSb) material has very attractive electronic and optoelectronic properties which are suitable for next-generation infrared (IR) photodetector applications. In this work, properties of undoped GaSb material such as density of states, bandstructure, electron density, absorption coefficient, dielectric function, refractive index, and extinction coefficient are calculated using density-functional theory (DFT). Moreover, the effects of doping with Ge, Sn, and Zn elements on these properties of GaSb material are investigated. It is found that undoped GaSb material exhibits a direct gap of ≈0.72 eV. Among different doping elements, Ge-doped GaSb produces a very significant enhancement in optical properties. The Ge-doped GaSb demonstrates a four times higher absorption coefficient in comparison to undoped GaSb in the IR region at 0.8 eV photon energy. GaSb-based photodetector device is designed using the Solar Cell Capacitance Simulator (SCAPS) 1D tool. The efficiency of the designed photodetector with optimum thicknesses and doping of different layers is found to be improved from 21.34% to 25.91% after incorporating the absorption data set obtained from the DFT calculations. Additionally, the photodetector with optimum parameters demonstrates maximum responsivity of value ≈0.31 A W−1. In the previous findings, it is demonstrated that GaSb is a very suitable material for next-generation IR photodetector applications. © 2023 Wiley-VCH GmbH.Item Indium Antimonide-Based All-Dielectric Metasurface Absorber at Terahertz Frequency for Refractive Index Sensing Applications(Institute of Electrical and Electronics Engineers Inc., 2024) Thomas, S.K.; Shenoy, A.; Satyanarayan, M.N.In this article, we present an indium antimonide (InSb)-based metasurface absorber (MA) using a complementary ring structure. The proposed MA exhibits absorption characteristics in the terahertz frequency range spanning from 1.0 to 2.2 THz. Within this frequency range, the MA demonstrates dual-band tunability, achieving approximately 100% absorption. Geometric parameters such as the outer ring radii, ring width, and InSb layer thickness are systematically adjusted to fine-tune the absorption frequency of the MA. In addition, we explore the refractive index sensing capabilities by introducing different refractive index materials into the air-filled complementary ring cavity. Notably, we achieve a peak refractive index sensitivity of 555 GHz per refractive index unit (RIU) for the first absorption peak at a minimum radius of 60 µm. © 2001-2012 IEEE.Item Unveiling the Potential of Cs3Sb2ClxI9-x-Based Solar Cells for Efficient Indoor Light Harvesting: Numerical Simulation(John Wiley and Sons Inc, 2024) Manjhi, S.; Siddharth, G.; Pandey, S.K.; Sengar, B.S.; Garg, V.Lead-free Perovskite-inspired materials (PIM) have become the most promising candidate for indoor photovoltaics (IPV) because of their low toxicity and high performance. In this study, the potential of one of the lead-free PIMs, Cesium antimony chloride iodide (Cs3Sb2ClxI9-x), is explored for IPV devices. Recent experimental research work on a Cs3Sb2ClxI9-x− based solar cell with a power conversion efficiency (PCE) of 3.7% is considered for the baseline model development. The device performance is further optimized by investigating 1) absorber thickness and defect density, 2) band alignment of Electron Transport Layer (ETL)/Absorber, ETL Doping concentration and absorber/ETL interface defect density, 3) band alignment of Hole Transport Layer (HTL)/Absorber, HTL Doping concentration, and absorber/HTL interface defect density, 4) work function of metal contacts, 5) series and shunt resistances. After device optimization, the simulated device under 1000 lux WLED is able to achieve Jsc, Voc, FF, and PCE of 1.8 mA cm−2, 1.46 V, 89.3%, and 45.05%, respectively. Further, an evaluation of the performance of the optimized device under various indoor light sources, including White Light Emitting Diode (WLED), halogen, and Compact Fluorescent Lamp (CFL), is conducted in order to assess its performance under widely utilized lighting conditions. © 2024 Wiley-VCH GmbH.Item Insights into the potential of Sb alloyed Cu2AgBiI6-based solar cells: For efficient indoor energy-harvesting(Elsevier Ltd, 2025) Kumar, A.; Siddharth, G.; Dwivedi, P.; Pandey, S.K.; Sengar, B.S.; Garg, V.Recently, indoor photovoltaics have attracted significant attention due to their remarkable capability to generate power from indoor light sources. This work investigates the performance of perovskite-inspired material Sb alloyed Cu2AgBiI6 (CABI-Sb) based indoor photovoltaic device, which has shown a power conversion efficiency of 9.53 %, reported in a recent experimental study by B. Al-Anesi et al. The baseline model of the CABI-Sb device structure (FTO/TiO2/CABI-Sb/Spiro-OMeTAD/Au) is developed in SCAPS-1D using the earlier reported experimental data. Baseline model parameters under WLED illumination are Jsc: 128.2 µA/cm2, Voc: 0.51 V, FF: 66.57 %, and PCE: 9.53 %, with a minor deviation of less than 1 %, which validates the developed model with experimental data. The performance of the device is fine-tuned by optimizing 1) Absorber thickness and defect density 2) Electron Transport Layer (ETL) doping density, conduction band offset (CBO) and interface defect density between the ETL/absorber (TiO2 /CABI-Sb) interface, 3) Hole Transport Layer (HTL) doping density, valence band offset (VBO) and interface defect density between HTL/absorber (CABI-Sb/Spiro-OMeTAD) interface, 4) work function of contacts, and 5) Series and shunt resistance were optimized. The performance parameters of the optimized device under the WLED illumination are Jsc: 1.84 mA/cm2, Voc: 1.60 V, FF: 86.78 %, and PCE: 49.31 %. A remarkable improvement in PCE is achieved from 9.53 % to 49.31 %. Further, to validate the suitability of the optimized device under different indoor environments, optimized device performance is evaluated under different lux intensities of WLED (6500 K), WLED (2700 K), compact fluorescent light (CFL), and halogen. © 2024 International Solar Energy SocietyItem An Intricate Balance of Ionicity and Covalency: Metal-Like Conduction in All-Inorganic Halide Double Perovskite Cs2AgSbCl6(American Chemical Society, 2025) Kalyani, M.; Ananthram, K.S.; Saha, S.; Ninawe, P.; Tarafder, K.; Ballav, N.Halide perovskites have recently evolved as attractive materials with enormous technological significance due to synthetic control over the structure-property relationship. Halide perovskites are often realized to be either electrical insulators or semiconductors. We present an unusual metal-like conduction (thermally deactivated) in a Pb-free all-inorganic halide double perovskite, Cs2AgSbCl6. The experimental results were understood using density functional theory studies, combined with molecular dynamics simulations and electron localization function calculations, revealing retention of the predominant ionicity of the Ag-Cl bond and an increase in the covalency of the Sb-Cl bond at an elevated temperature, which resulted in a significant change of the electronic band structure, including the density of states, thereby exhibiting an intricate balance of ionicity and covalency. A significant modulation of the electrical conductivity (more than 3 orders of magnitude) without any noticeable structural change will stimulate the investigation of hitherto unknown electronic phase transitions in halide double perovskites. Additionally, light-induced unidirectional rectification of current in Cs2AgSbCl6 was ascribed to a dynamic internal polarization effect. © 2025 American Chemical Society.Item Defect-engineered single crystal Bi2Te3 via Sb and Se doping for enhanced thermoelectric performance(Springer, 2025) Puthran, S.; Hegde, G.S.; Prabhu, A.N.; Wang, Y.-L.; Kuo, Y.K.; Joshi, S.; Udayashankar, N.K.; Nayak, R.The limitation of the single crystal melt growth method to tune the microstructure of the materials in a controlled way and the need for enhancing the thermoelectric properties of single crystal grown Bismuth telluride (Bi2Te3), through defect and microstructural engineering, has motivated this work. In this work, we address this limitation through a controlled doping strategy using antimony (Sb) and selenium (Se) to introduce targeted defects and microstructural modifications within single-crystalline Bi2Te3. Sb and Se substitutions create atomic scale strain, point defects, and micro-grain structures, enhancing phonon scattering without significantly disrupting the crystalline order. The resulting defect-engineered single crystals exhibit improved thermoelectric performance, with a notable reduction in lattice thermal conductivity and retention of excellent electrical properties. The co-doped compositions, Bi2Te2.7Se0.3 and (Bi0.98Sb0.02)2Te2.7Se0.3, exhibited significantly enhanced thermoelectric performance, with Seebeck coefficients reaching ~ 253 ?V/K and ? 211 ?V/K, respectively, over the 10–400 K range. The power factor improved remarkably, showing a ~ 30-fold increase for Bi2Te2.7Se0.3 and ~ 20-fold for the Sb-doped variant, while the figure of merit (ZT) improved by ~ 28.5 and ~ 14 times, respectively. Further, a flexible thermoelectric device fabricated from these optimized materials generated output power of 2.7 nW and 3.35 nW at ambient temperature. The non-monotonic variation of the Seebeck coefficient with Sb content, showing an optimal enhancement at x = 0.04, highlights the delicate balance between carrier concentration and band structure modification, emphasizing moderate Sb substitution achieves the most favorable conditions for thermoelectric performance. Our results present a scalable strategy for bridging the performance gap between pristine single crystals and heavily nanostructured thermoelectrics, opening new avenues for high-efficiency energy harvesting devices. © The Author(s) 2025.Item Optimizing thermoelectric properties of Bi2Te3 via Sb and Se Co-doping: experimental insights and finite elemental simulations using COMSOL(Springer, 2025) Puthran, S.; Prabhu, A.N.; Kamble, M.; Babu, P.D.; Joshi, S.; Udayashankar, N.K.In this study, we investigated the impact of antimony (Sb) and selenium (Se) co-dopants on the thermoelectric properties of bismuth telluride (Bi2Te3). Our findings reveal that Sb doping significantly enhances the electrical conductivity of the material, increasing it by a factor of 2.83 for (Bi0.98Sb0.02)2Te2.7Se0.3, primarily due to an increase in carrier concentration. The electrical resistivity of pristine Bi2Te3 at 300 K is 2.79 × 10?4 ?·m, which decreases substantially to 0.006 × 10?4 ?·m at 303 K with Sb doping at x = 0.02. Additionally, (Bi0.96Sb0.04)2Te2.7Se0.3 composition achieves the highest power factor of 9.744 × 10?5 W/m·K2 at 300 K, a 3-times improvement over the pristine Bi2Te3 (3.143 × 10?5 W/m·K2). The ZT value of Bi2Te2.7Se0.3 is 3.5 times higher than that of the pristine material at 350 K. COMSOL simulations support the experimental findings, revealing a maximum temperature gradient of 35 °C (hot end: 20 °C, cold end: ? 15 °C) for the (Bi0.98Sb0.02)2Te2.7Se0.3 module with comparable p-type and n-type parameters. The increased temperature gradient in the COMSOL simulation correlates with the improved thermoelectric performance observed experimentally, indicating that co-doping Bi2Te3 with Sb and Se effectively enhances its thermoelectric properties. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2025.