International Journal of Physics | Vol. 8, No. 6, June 2017 | pp. 41–48
DOI: 10.46882/2017/IJP/000086
Research Article
Title: Quantum Efficiency Optimization of Tin-Based Perovskite Solar Cells via Graded Bandgap Profiling
Names of Authors: H. K. Tanaka¹, S. P. McCarthy²
Authors’ Affiliations: ¹Department of Quantum Engineering, Nagoya University, Nagoya, Japan; ²European Organization for Nuclear Research (CERN), Geneva, Switzerland
Abstract: Lead-free tin-based perovskite solar cells present a highly promising, environmentally friendly pathway for low-cost, high-efficiency photovoltaics. This paper presents a comprehensive numerical model to optimize the internal quantum efficiency of methylammonium tin iodide (MASnI3) perovskite solar cells using a graded bandgap design. We systematically evaluated the impacts of carrier recombination lifetimes and interface defect densities on device performance parameters under standard one-sun illumination (AM 1.5G, 100.0 mW/cm²). Our numerical calculations reveal that grading the iodine-to-bromine ratio creates a linear bandgap profile (varying from 1.30 eV to 1.65 eV), which generates a built-in electric field. This built-in field accelerates charge separation and reduces radiative recombination rates. When standard recombination lifetimes of 15.0 ns are introduced, the optimized graded device yields a short-circuit current density of 28.4 mA/cm² and an open-circuit voltage of 0.88 V. This results in a maximum power conversion efficiency of 18.4%, representing a significant improvement over the 13.2% efficiency calculated for the uniform bandgap control cell. We also analyzed the thermal stability of the device between 280.0 K and 360.0 K, demonstrating that the graded structure reduces thermal efficiency degradation by 25.0%. These insights provide practical guidelines for engineering high-performance, eco-friendly photovoltaics.
Keywords: Perovskite solar cells; graded bandgap; quantum efficiency; charge transport; numerical modeling; tin-based photovoltaics
Manuscript Timeline: Received: March 02, 2017; Revised: April 14, 2017; Accepted: May 02, 2017; Published: June 12, 2017
Citation: Tanaka, H. K., & McCarthy, S. P. (2017). Quantum Efficiency Optimization of Tin-Based Perovskite Solar Cells via Graded Bandgap Profiling. International Journal of Physics, 8(6), 41–48.
International Journal of Physics | Vol. 8, No. 5, May 2017 | pp. 33–40
DOI: 10.46882/2017/IJP/000085
Research Article
Title: Thermal Conductance Degradation and Phonon Transport across Carbon Nanotube-Copper Interfaces
Names of Authors: D. W. Meyer¹, J. R. Weber²
Authors’ Affiliations: ¹Institute of Physics, Karlsruher Institut für Technologie, Karlsruhe, Germany; ²Physik-Department, Technische Universität München, Garching, Germany
Abstract: Dissipating heat efficiently across highly mismatched material boundaries remains a core technological challenge in modern high-power nanoelectronics and structural composites. This paper uses molecular dynamics simulations to quantify thermal conductance degradation and track phonon wavepacket scattering dynamics at defective carbon nanotube-copper (CNT-Cu) junctions. We constructed atomistic models using the optimized Tersoff and embedded-atom method potentials, incorporating varying concentrations of interfacial point defects and vacancy networks. Longitudinal and transverse acoustic phonon wavepackets were generated with narrow frequency spreads centered between 2.0 THz and 10.0 THz. The computational data demonstrate that high-frequency acoustic phonons (f greater than 5.5 THz) undergo severe diffuse scattering at the defective boundary layer, dropping the transmission coefficient from 0.68 down to 0.15. This diffuse scattering behavior is driven by localized strain fields and localized interface vibrational modes. The overall interfacial thermal conductance was calculated to decrease by 55.0% when the interfacial defect density scaled from 1.0% to 5.0% at an equilibrium temperature of 300.0 K. These molecular dynamics calculations clarify the atomic-scale mechanisms restricting heat carrier propagation, helping engineers design targeted thermal management solutions for carbon-metal hybrids.
Keywords: Thermal conductance; phonon scattering; molecular dynamics; carbon nanotube; copper interface; nanoelectronics
Manuscript Timeline: Received: February 11, 2017; Revised: March 24, 2017; Accepted: April 10, 2017; Published: May 16, 2017
Citation: Meyer, D. W., & Weber, J. R. (2017). Thermal Conductance Degradation and Phonon Transport across Carbon Nanotube-Copper Interfaces. International Journal of Physics, 8(5), 33–40.
International Journal of Physics | Vol. 8, No. 4, April 2017 | pp. 25–32
DOI: 10.46882/2017/IJP/000084
Research Article
Title: Relativistic Hydrodynamic Evolution and Elliptic Flow Anomalies in Asymmetric Oxygen-Gold Collisions
Names of Authors: S. C. O’Brien¹, L. M. Dupont²
Authors’ Affiliations: ¹School of Physics, University College Dublin, Dublin, Ireland; ²Laboratoire de Geologie de Lyon, Ecole Normale Superieure de Lyon, Lyon, France
Abstract: High-energy asymmetric collisions provide a unique experimental testing ground to study the spatial geometry limits required to form a droplet of quark-gluon plasma. This study presents a relativistic hydrodynamic modeling framework to simulate particle production cascades and evaluate elliptic flow anomalies in oxygen-gold (O-Au) collisions at a center-of-mass energy of 200.0 GeV per nucleon pair. We utilized a 3+1 dimensional viscous hydrodynamic code coupled with a statistical hadronization module to compute transverse momentum spectra. The initial energy density profiles were generated using a Monte Carlo Glauber model to capture sub-nucleon scale configurations. The numerical simulations show that expanding systems build a substantial radial flow profile, shifting the mean transverse momentum of pions up to 0.78 GeV/c in high-multiplicity events. The calculated elliptic flow coefficient (v²) displays a strong mass-ordering effect, which matches experimental measurements gathered by specialized nuclear physics detectors within a ±5.5% margin. This close agreement suggests that small-scale systems generated in O-Au collisions can achieve brief hydrodynamic collective expansion. These findings help clarify the boundaries of fluid-like behavior in high-energy subatomic particle interactions.
Keywords: Relativistic hydrodynamics; particle production; oxygen-gold collisions; elliptic flow; Glauber model; statistical hadronization
Manuscript Timeline: Received: January 08, 2017; Revised: February 17, 2017; Accepted: March 05, 2017; Published: April 12, 2017
Citation: O’Brien, S. C., & Dupont, L. M. (2017). Relativistic Hydrodynamic Evolution and Elliptic Flow Anomalies in Asymmetric Oxygen-Gold Collisions. International Journal of Physics, 8(4), 25–32.
International Journal of Physics | Vol. 8, No. 3, March 2017 | pp. 17–24
DOI: 10.46882/2017/IJP/000083
Research Article
Title: Kinetic Modelling of Electron Transport Parameters and Reaction Rates in Acetylene-Hydrogen Discharges
Names of Authors: D. L. Santos¹, S. H. Zhang²
Authors’ Affiliations: ¹Department of Physics, University of Coimbra, Coimbra, Portugal; ²Department of Physics, Tsinghua University, Beijing, China
Abstract: Acetylene-hydrogen (C2H2-H2) gas discharges are widely used in the material processing industries to deposit high-quality diamond-like carbon thin films and carbon nanotubes. This paper develops a self-consistent kinetic model to evaluate electron transport parameters and calculate ionization coefficients in low-pressure acetylene-hydrogen mixtures. We solved the electron Boltzmann equation using a multi-term spherical harmonic expansion framework across a wide reduced electric field range (E/N) from 5.0 Td to 600.0 Td. The cross-section dataset included elastic momentum transfer, rotational, vibrational excitation, dissociative attachment, and direct impact ionization processes. Our modeling results show that adding small fractions of acetylene (from 2.0% to 10.0% by volume) drastically distorts the electron energy distribution function. At E/N = 60.0 Td, the total dissociation rate coefficient increases by an order of magnitude due to the low threshold energy of acetylene vibrational modes. The calculated electron drift velocities and diffusion coefficients match independent swarm experimental measurements within a tight ±5.0% variance. These kinetic parameters provide essential input data for optimizing industrial chemical vapor deposition reactors.
Keywords: Acetylene plasmas; Boltzmann equation; electron transport; ionization coefficient; carbon deposition; cross-section
Manuscript Timeline: Received: December 14, 2016; Revised: January 20, 2017; Accepted: February 08, 2017; Published: March 15, 2017
Citation: Santos, D. L., & Zhang, S. H. (2017). Kinetic Modelling of Electron Transport Parameters and Reaction Rates in Acetylene-Hydrogen Discharges. International Journal of Physics, 8(3), 17–24.
International Journal of Physics | Vol. 8, No. 2, February 2017 | pp. 9–16
DOI: 10.46882/2017/IJP/000082
Research Article
Title: Topological Bound States and Robust Electronic Transport in Bismuth-Modified Graphene Ribbons
Names of Authors: J. W. Park¹, E. C. Vance²
Authors’ Affiliations: ¹Department of Physics, Korea Advanced Institute of Science and Technology, Daejeon, South Korea; ²Department of Physics, University of California, Berkeley, California, USA
Abstract: Quantum spin Hall insulators provide an innovative pathway for developing low-power electronics by supporting backscattering-immune spin transport along their boundaries. This study designs and simulates topological bound states and robust spin transport within a two-dimensional honeycombed lattice of bismuth-modified graphene nanoribbons. We computed the electronic band structures using the relativistic tight-binding method across the Brillouin zone. The strong intrinsic spin-orbit coupling induced by bismuth atoms breaks the electronic degeneracy at the Dirac valleys, creating a bulk topological band gap with a width of 0.22 eV. We calculated a non-zero spin Chern number of Cs = +1, verifying the non-trivial topological character of the system. To demonstrate transport robustness, we simulated spin-polarized electron wavepacket propagation past single-atom vacancies and line defect boundaries. The edge mode bypassed these structural obstacles with a high transmission efficiency of 99.5% ± 0.2%, showing zero backscattering due to time-reversal symmetry protections. These findings provide solid engineering targets for building backscattering-immune spintronic transistors, quantum data pathways, and integrated spin-logic circuits.
Keywords: Topological insulators; quantum spin Hall effect; spin-orbit coupling; tight-binding method; edge states; spintronics
Manuscript Timeline: Received: November 05, 2016; Revised: December 18, 2016; Accepted: January 11, 2017; Published: February 15, 2017
Citation: Park, J. W., & Vance, E. C. (2017). Topological Bound States and Robust Electronic Transport in Bismuth-Modified Graphene Ribbons. International Journal of Physics, 8(2), 9–16.
International Journal of Physics | Vol. 8, No. 1, January 2017 | pp. 1–8
DOI: 10.46882/2017/IJP/000081
Research Article
Title: Elasticity Profiles and High-Pressure Structural Transitions in Ultra-Incompressible Molybdenum Diboride
Names of Authors: V. I. Morozov¹, O. B. Ivanov²
Authors’ Affiliations: ¹Institute of High Pressure Physics, Russian Academy of Sciences, Troitsk, Russia; ²L.D. Landau Institute for Theoretical Physics, Russian Academy of Sciences, Chernogolovka, Russia
Abstract: Developing ultra-incompressible structural materials capable of operating under extreme mechanical stress is vital for specialized industrial machining and deep-earth simulation components. This paper investigates the high-pressure elastic profiles and monitors structural phase transitions in hexagonal molybdenum diboride (MoB²) up to hydrostatic pressures of 150.0 GPa. We performed first-principles density functional theory computations within the generalized gradient approximation framework. At zero pressure, the calculated bulk modulus is B0 = 315.0 GPa, with an elastic pressure derivative value of B0' = 4.10, matching experimental diamond anvil cell measurements within a 1.2% margin. The single-crystal elastic constants (C11, C33, C44, C12, and C13) increase monotonically under uniform compression, satisfying all Born mechanical stability parameters across the entire pressure range. The directional compressibility paths reveal that the crystal c-axis displays exceptional stiffness due to short, covalent molybdenum-boron bonds. Electronic structure computations show a high density of states at the Fermi level, indicating that MoB² maintains its metallic profile under ultra-high pressures. These precise elastic records confirm the viability of transition metal borides as robust alternatives to conventional superhard diamond materials.
Keywords: Molybdenum diboride; density functional theory; elastic constants; high pressure; structural stability; mechanical properties
Manuscript Timeline: Received: October 12, 2016; Revised: November 27, 2016; Accepted: December 15, 2016; Published: January 16, 2017
Citation: Morozov, V. I., & Ivanov, O. B. (2017). Elasticity Profiles and High-Pressure Structural Transitions in Ultra-Incompressible Molybdenum Diboride. International Journal of Physics, 8(1), 1–8.