Srihari Kastuar

Srihari Kastuar

Computational Condensed Matter Physics | Machine Learning

Publications

Chemically tuned intermediate band states in atomically thin Cu$_x$GeSe/SnS quantum material for photovoltaic applications

Published in Science Advances, 2024

A new generation of quantum material derived from intercalating zerovalent atoms such as Cu into the intrinsic van der Waals gap at the interface of atomically thin two-dimensional GeSe/SnS heterostructure is designed, and their optoelectronic features are explored for next-generation photovoltaic applications. Advanced ab initio modeling reveals that many-body effects induce intermediate band (IB) states, with subband gaps (~0.78 and 1.26 electron volts) ideal for next-generation solar devices, which promise efficiency greater than the Shockley-Queisser limit of ~32%. The charge carriers across the heterojunction are both energetically and spontaneously spatially confined, reducing nonradiative recombination and boosting quantum efficiency. Using this IB material in a solar cell prototype enhances absorption and carrier generation in the near-infrared to visible light range. Tuning the active layer’s thickness increases optical activity at wavelengths greater than 600 nm, achieving ~190% external quantum efficiency over a broad solar wavelength range, underscoring its potential in advanced photovoltaic technology.

Recommended citation: Srihari M. Kastuar, Chinedu E. Ekuma, Chemically tuned intermediate band states in atomically thin CuxGeSe/SnS quantum material for photovoltaic applications. Sci. Adv. 10, eadl6752(2024). DOI: 10.1126/sciadv.adl6752

Giant electrophotonic response in two-dimensional halide perovskite Cs3Bi2I9 by strain engineering

Published in Physical Review Materials, 2023

Organic-inorganic mixed halide perovskites have been of utmost importance for renewable energy and information technology due to their outstanding properties, but the toxicity of Pb and the instability of the organic component has hindered their applications. Herein, we present detailed mechanical and elastic properties of the family of the Pb-free perovskite-derived two-dimensional (2D) A3B2X9 (A=K,Rb,Cs;B=Bi,Sb,As,P; and X = Cl, Br, I), and demonstrate different physical property tunability of the archetypical Cs3 Bi2 I9 using ab initio simulations. Our calculated properties show that the optoelectronic properties can be tuned efficiently, as evidenced by flat bands in the band structure and the large absorption peaks in the optical spectra. Through strain engineering, we achieve a redshift of the optical absorption towards the visible regime and demonstrate a robust tuning of the optoelectronic properties for device applications.

Recommended citation: Kastuar, S. M., & Ekuma, C. E. (2023). Giant electrophotonic response in two-dimensional halide perovskite Cs3Bi2I9 by strain engineering. Physical Review Materials, 7(2), 024002.

Efficient prediction of temperature-dependent elastic and mechanical properties of 2D materials

Published in Scientific Reports, 2022

An efficient automated toolkit for predicting the mechanical properties of materials can accelerate new materials design and discovery; this process often involves screening large configurational space in high-throughput calculations. Herein, we present the ElasTool toolkit for these applications. In particular, we use the ElasTool to study diversity of 2D materials and heterostructures including their temperature-dependent mechanical properties, and developed a machine learning algorithm for exploring predicted properties.

Recommended citation: Kastuar, S. M., Ekuma, C. E., & Liu, Z. L. (2022). Efficient prediction of temperature-dependent elastic and mechanical properties of 2D materials. Scientific Reports, 12(1), 3776.

Blue phosphorene nanosheets with point defects: Electronic structure and hydrogen storage capability

Published in Applied Surface Science, 2021

Presence of defects in two dimensional nanomaterial can lead to dramatic changes in their structural and electronic properties. Through ab-initio DFT computations, we study the electronic structure of semiconducting 2D elemental monolayers of blue phosphorene, with common point defects like Stone-Wales, single and double vacancies. The calculated formation energies of single and double vacancies in phosphorene are found to be lower compared to other well known 2D monolayers. Electronic structure of blue phosphorene shows a reduced band gap from that of the perfect lattice, and flat bands characterizing the defect states. We also investigate the suitability of defective blue phosphorene as a hydrogen storage template. We find that, like in the case of perfect phosphorene nanosheets, metal decoration of defective phosphorene can enhance the storage capacity for hydrogen molecules, with binding energies suitable for practical storage. Lithium decoration of the single and double vacancy defect at higher coverage can store a maximum of six to nine hydrogen molecules per defect, thus leading to a high gravimetric density of hydrogen. It is found that these structures are stable at room temperature. Comparing the storage capabilities of defective black and blue phosphorene, we find that defective blue phosphorene can store more hydrogen than black phosphorene.

Recommended citation: John, D., Nharangatt, B., Kastuar, S. M., & Chatanathodi, R. (2021). Blue phosphorene nanosheets with point defects: Electronic structure and hydrogen storage capability. Applied Surface Science, 551, 149363.