arXiv subjects

Guocai Liu

Publications and source records attributed to Guocai Liu.

8 recordsLinked to original sources

arXiv2026

The Role of Hydrogen and Oxygen Interstitial Defects in Crystalline Si cells: Mechanism of Device Degradation in Humid Environment

The efficiency of silicon solar cells gradually decreases in various environments, with humidity being a key factor contributing to this decline through moisture-induced degradation (MID) involving multiple mechanisms including encapsulant hydrolysis and metal ion migration. Among these mechanisms, the role of water-derived hydrogen and oxygen interstitial defects represents an underexplored yet fundamental degradation pathway. This study employs density functional theory and quantum transport theory to investigate hydrogen and oxygen interstitial defects as a novel perspective for understanding MID mechanisms. Results reveal that neutral hydrogen interstitials at bond-center sites exhibit low diffusion barriers (0.96 eV) and act as deep-level recombination centers, while oxygen interstitials face higher diffusion barriers (2.2 eV) with limited trapping capability. Device simulations demonstrate that hydrogen defects cause substantially more pronounced photovoltaic current degradation through enhanced non-radiative recombination. Critically, under humid conditions, hydrogen from water molecules readily penetrates silicon lattices forming active recombination centers, while oxygen incorporation remains kinetically limited with negligible impact. This interstitial defect perspective provides novel understanding of MID mechanisms, explaining why moisture exposure primarily degrades silicon solar cells through hydrogen rather than oxygen incorporation, offering fundamental insights for developing targeted mitigation strategies.

cond-mat.mtrl-sci↗

arXiv2022

MyoPS: A Benchmark of Myocardial Pathology Segmentation Combining Three-Sequence Cardiac Magnetic Resonance Images

Assessment of myocardial viability is essential in diagnosis and treatment management of patients suffering from myocardial infarction, and classification of pathology on myocardium is the key to this assessment. This work defines a new task of medical image analysis, i.e., to perform myocardial pathology segmentation (MyoPS) combining three-sequence cardiac magnetic resonance (CMR) images, which was first proposed in the MyoPS challenge, in conjunction with MICCAI 2020. The challenge provided 45 paired and pre-aligned CMR images, allowing algorithms to combine the complementary information from the three CMR sequences for pathology segmentation. In this article, we provide details of the challenge, survey the works from fifteen participants and interpret their methods according to five aspects, i.e., preprocessing, data augmentation, learning strategy, model architecture and post-processing. In addition, we analyze the results with respect to different factors, in order to examine the key obstacles and explore potential of solutions, as well as to provide a benchmark for future research. We conclude that while promising results have been reported, the research is still in the early stage, and more in-depth exploration is needed before a successful application to the clinics. Note that MyoPS data and evaluation tool continue to be publicly available upon registration via its homepage (www.sdspeople.fudan.edu.cn/zhuangxiahai/0/myops20/).

eess.IV↗

arXiv2020

Inorganic photovoltaic cells based on BiFeO3: spontaneous polarization, lattice matching, light polarization and their relationship to photovoltaic performance

Inorganic ferroelectric perovskite oxides are more stable than hybrid perovskites. However, their solar energy harvest efficiency is not so good. Here, by constructing a series of BiFeO3 based devices (solar cells), we investigated three factors that influence the photovoltaic performance, including spontaneous polarization, terminated ions species in the interface between BiFeO3 and the electrode, and polarized light irradiation. This work was carried out in the framework of density functional theory combined with non-equilibrium Green's function theory under built in electric field or finite bias. The results showed that 1. the photocurrent is larger only under a suitable electronic band gap rather than larger spontaneous polarization; 2. the photocurrent reaches the largest in Bi ions terminated interface than in the case of Fe ion or O ion with SrTiO3 electrode; 3. the photocurrent could be largely enhanced if the polarized direction of the monochromatic light is perpendicular to the spontaneous polarization direction. The results would deepen the understanding of some experimental results of BiFeO3 based solar cells.

cond-mat.mtrl-sci↗

arXiv2015

Quantum Hall Effects in a Non-Abelian Honeycomb Lattice

We study the tunable quantum Hall effects in a non-Abelian honeycomb optical lattice which is a many-Dirac-points system. We find that the quantum Hall effects present different features as change as relative strengths of several perturbations. Namely, a gauge-field-dressed next-nearest-neighbor hopping can induce the quantum spin Hall effect and a Zeeman field can induce a so-called quantum anomalous valley Hall effect which includes two copies of quantum Hall states with opposite Chern numbers and counter-propagating edge states. Our study extends the borders of the field of quantum Hall effects in honeycomb optical lattice when the internal valley degrees of freedom enlarge.

cond-mat.str-el↗

arXiv2013

Chiral f-wave Topological Superuid in Triangular Optical Lattices

We demonstrate that an exotically chiral f-wave topological superfluid can be induced in coldfermionic-atom triangular optical lattices through the laser-field-generated effective non-Abelian gauge field, controllable Zeeman fields and s-wave Feshbach resonance. We find that the chiral f-wave topological superfluid is characterized by three gapless Majorana edge states located on the boundary of the system. More interestingly, these Majorana edge states degenerate into one Majorana fermion bound to each vortex in the superfluid. Our proposal enlarges topological superfluid family and specifies a unique experimentally controllable system to study the Majorana fermion physics.

cond-mat.quant-gas↗

arXiv2012

Topological Superfluid Transition Induced by Periodically Driven Optical Lattice

We propose a scenario to create topological superfluid in a periodically driven two-dimensional square optical lattice. We study the phase diagram of a spin-orbit coupled s-wave pairing superfluid in a periodically driven two-dimensional square optical lattice. We find that a phase transition from a trivial superfluid to a topological superfluid occurs when the potentials of the optical lattices are periodically changed. The topological phase is called Floquet topological superfluid and can host Majorana fermions.

cond-mat.mes-hall↗

arXiv2010

Simulating and Detecting the Quantum Spin Hall Effect in Kagomé Optical Lattice

We propose a model which includes a nearest-neighbor intrinsic spin-orbit coupling and a dimer Hamiltonian in the Kagomé lattice and promises to host the transition from the quantum spin Hall insulator to the normal insulator. In addition, we design an experimental scheme to simulate and detect this transition in the ultracold atom system. The lattice intrinsic spin-orbit coupling is generated via the laser-induced-gauge-field method. Furthermore, we establish the connection between the spin Chern number and the spin-atomic density which enables us to detect the topological quantum spin Hall insulator directly by the standard density-profile technique used in the atomic systems.

cond-mat.mes-hall↗

arXiv2008

Spin Hall effect in the kagome lattice with Rashba spin-orbit interaction

We study the spin Hall effect in the kagomé lattice with Rashba spin-orbit coupling. The conserved spin Hall conductance $σ_{xy}^{s}$ (see text) and its two components, i.e., the conventional term $σ_{xy}^{s0}$ and the spin-torque-dipole term $σ_{xy}^{sτ}$, are numerically calculated, which show a series of plateaus as a function of the electron Fermi energy $ε_{F}$. A consistent two-band analysis, as well as a Berry-phase interpretation, is also given. We show that these plateaus are a consequence of the various Fermi-surface topologies when tuning $ε_{F}$. In particular, we predict that compared to the case with the Fermi surface encircling the $\mathbfΓ$ point in the Brillouin zone, the amplitude of the spin Hall conductance with the Fermi surface encircling the $\mathbf{K}$ points is twice enhanced, which makes it highly meaningful in the future to systematically carry out studies of the $\mathbf{K}$-valley spintronics.

cond-mat.mes-hall↗