Binyi Qin

In this study, the vibrational modes of nitrofurantoin, urea, and cocrystal were characterized by terahertz time domain spectroscopy and Raman spectroscopy. The results indicate that both terahertz and Raman spectroscopy can effectively identify cocrystal and parent materials, with terahertz spectroscopy being more prominent. Meanwhile, the vibrational modes and structural optimization of four theoretical cocrystal configurations of the two drugs were simulated by density functional theory (DFT). Comparing the theoretical results with the experimental results shows that theoretical configuration D is most consistent with the experimental results. The results provide rich information on the pharmaceutical cocrystal to improve the physicochemical properties and pharmacological activities of specific pharmaceuticals at the molecular level. It shows that terahertz and Raman vibrational spectroscopy combined with DFT calculated is an effective method to analyze weak intermolecular interactions and characterize the molecules with cocrystal.

Pharmaceutical co-crystals present a promising avenue for enhancing the physicochemical properties of active pharmaceutical ingredients by modifying intermolecular interactions among raw materials. Theophylline, a methylpurine drug commonly used in respiratory treatments, has limited bioavailability in vivo due to its poor water solubility. In this study, a theophylline-nicotinamide co-crystal was successfully synthesized using the solid-state grinding method. Both the parent materials and the theophylline-nicotinamide co-crystal were characterized using terahertz and Raman spectroscopy. The terahertz spectra exhibited significant differences in the absorption peak between the experimental co-crystal and the parent materials, which were further corroborated by similar findings in the Raman spectra. Additionally, density functional theory was employed to optimize the structure of the theophylline-nicotinamide co-crystal and identify its corresponding vibrational modes. Furthermore, intermolecular interactions were analyzed through the independent gradient model based on Hirshfeld partition analysis and Hirshfeld surface analysis. The results demonstrate that the integration of terahertz and Raman spectroscopy with theoretical calculations provides valuable insights into the molecular-level formation of co-crystals. This approach offers crucial information for the analysis of weak interactions in pharmaceutical co-crystals, which is essential for their design and optimization.

In the prosperous development of terahertz (THz) metamaterials, Fano resonances have gained attention due to their potential applications in ultrasensitive systems. The performance of Fano resonance is directly influenced by the geometrical parameters of the element structure. However, the traditional design rules for Fano resonances in metamaterials rely on an empirical trial-and-error strategy, necessitating significant effort to achieve optimal results. To address this issue, we propose a design method in this study that utilizes the finite integration technique in time domain (FITD) along with a multi-objective optimization genetic algorithm for the intelligent design of metamaterial structures exhibiting the Fano resonance phenomenon. The FITD method is primarily used to calculate the Fano resonance with different metamaterial geometric structure parameters, while the genetic algorithm efficiently selects the optimal solution. Our method, characterized by high efficiency and complete independence from prior knowledge, could offer a new design technique for metamaterials with specific functions, thereby contributing to the development of THz applications.

Benefiting from the advantages of a high absorption coefficient, a long charge diffusion length, excellent carrier mobility, and a tunable bandgap, three-dimensional (3D) metal halide perovskites exhibit great potential for application in solar cells. However, 3D perovskite solar cells (PSCs) often suffer from poor long-term stability against moisture, heat, and light. To address this issue, reducing the dimension of perovskite and forming two-dimensional (2D) perovskites can be effective in slowing down the oxidation of the perovskite film and significantly improving device stability. In this study, 2D PSCs were designed with glass/FTO/TiO₂/Dion–Jacobson (DJ) perovskite/NiOx/Au structures, based on the solar cell simulation software SCAPS. The absorption layers employed in the study included PeDAMA₂Pb₃I₁₀, PeDAMA₃Pb₄I₁₃, PeDAMA₄Pb₅I₁₆, and PeDAMA₅Pb₆I₁₉. The influence of the conduction band offset (CBO) variation in the range of −0.5 to 0.5 eV on cell performance was explored through a numerical simulation. The simulation results indicate that the open-circuit voltage and fill factor continue to increase, whereas the short-circuit current density remains almost unchanged when the CBO increases from −0.5 eV to 0 eV. The devices exhibit better performance when the value of the CBO is positive and within a small range. For DJ PSCs, controlling the CBO within 0.1–0.4 eV is conducive to better cell performance.

A high-speed and high-sensitivity avalanche photodetector (APD) is a critical component of a high-data-rate and low-power optical-communication link. In this paper, we study a high-speed and high-efficiency Ge/Si heterostructure APD. First, we numerically study the speed performance of the APD by analyzing frequency response. An optimized epitaxial structure of the high-speed APD is designed. In the absence of RC time effects, the APD exhibits a fast pulse response (full-width at half-maximum) of 10 ps and a high 3 dB bandwidth of 33 GHz at a high-gain value of 10. Taking device size and the corresponding RC time effects into account, the APD still achieves a high 3 dB bandwidth of 29 GHz at a gain value of 10. Moreover, a novel subwavelength periodic hole array is designed on the normal-incidence APD for enhancing light absorption without sacrificing speed performance. Near-perfect absorption is almost achieved by an infinite-period hole array due to the coupling of dual-resonance modes. A high-absorption efficiency of 64% is obtained by a limited-sized hole array in the high-speed APD. This work provides a promising method to design high-speed and high-efficiency normal-incidence Ge/Si heterostructure APDs for optical interconnect systems.

Although perovskite solar cells have achieved excellent photoelectric conversion efficiencies, there are still some shortcomings, such as defects inside and at the interface as well as energy level dislocation, which may lead to non-radiative recombination and reduce stability. Therefore, in this study, a double electron transport layer (ETL) structure of FTO/TiO₂/ZnO/(FAPbI₃)_0.85(MAPbBr₃)_0.15/Spiro-OMeTAD is investigated and compared with single ETL structures of FTO/TiO₂/(FAPbI₃)_0.85(MAPbBr₃)_0.15/Spiro-OMeTAD and FTO/ZnO/(FAPbI₃)_0.85(MAPbBr₃)_0.15/Spiro-OMeTAD using the SCAPS-1D simulation software, with special attention paid to the defect density in the perovskite active layer, defect density at the interface between the ETL and the perovskite active layer, and temperature. Simulation results reveal that the proposed double ETL structure could effectively reduce the energy level dislocation and inhibit the non-radiative recombination. The increases in the defect density in the perovskite active layer, the defect density at the interface between the ETL and the perovskite active layer, and the temperature all facilitate carrier recombination. Compared with the single ETL structure, the double ETL structure has a higher tolerance for defect density and temperature. The simulation outcomes also confirm the possibility of preparing a stable perovskite solar cell.

To broaden the absorption spectrum of cells, enhance the cell stability, and avoid high costs, a novel perovskite solar cell (PSC) with the structure of fluorine-doped tin oxide (FTO)/ZnO/CsPbI₃/FAPbI₃/CuSCN/Au is designed using the solar cell capacitance simulator (SCAPS) software. The simulation results indicate that the CsPbI₃/FAPbI₃ heterojunction PSC has higher quantum efficiency (QE) characteristics than the single-junction CsPbI₃-based PSC, and it outputs a higher short-circuit current density (J_sc) and power conversion efficiency (PCE). In order to optimize the device performance, several critical device parameters, including the thickness and defect density of both the CsPbI₃ and FAPbI₃ layers, the work function of the contact electrodes, and the operating temperature are systematically investigated. Through the optimum analysis, the thicknesses of CsPbI₃ and FAPbI₃ are optimized to be 100 and 700 nm, respectively, so that the cell could absorb photons more sufficiently without an excessively high recombination rate, and the cell achieved the highest PCE. The defect densities of CsPbI₃ and FAPbI₃ are set to 10¹² cm⁻³ to effectively avoid the excessive carrier recombination centering on the cell to increase the carrier lifetime. Additionally, we found that when the work function of the metal back electrode is greater than 4.8 eV and FTO with a work function of 4.4 eV is selected as the front electrode, the excessively high Schottky barrier could be avoided and the collection of photogenerated carriers could be promoted. In addition, the operating temperature is proportional to the carrier recombination rate, and an excessively high temperature could inhibit V_oc. After implementing the optimized parameters, the cell performance of the studied solar cell was improved. Its PCE reaches 28.75%, which is higher than most of existing solar cells. Moreover, the open circuit voltage (V_oc), J_sc, and PCE are increased by 17%, 9.5%, and 25.1%, respectively. The results of this paper provide a methodology and approach for the construction of high-efficiency heterojunction PSCs.

Terahertz wave modulation properties of graphene are investigated using an external 975 nm continuous wave laser. The modulation depth of monolayer graphene and 3-layer graphene was 16% and 32% under 1495 mW excitation power.

A four-peak terahertz metamaterial sensor was used to detect the reaction between different concentrations of vitamin B 6 ( V B 6 ) and bovine serum albumin (BSA), which achieves a concentration range (0.015–0.125 mg/µl) of V B 6 and a maximum binding concentration (0.05 mg/µl) of V B 6 and 0.0875 mg/µl BSA. To understand the combination of V B 6 and BSA, the reactants between VB ( V B 1 , V B 3 , and V B 5 ) with the same concentration (0.05 mg/µl) and a BSA solution with a concentration of 0.0875 mg/µl were carried on the surface of the sensor. Experimental results show that the reactants cause the four resonance peaks of the sensor to produce the coincident redshift, which is the same as the order of their binding coefficients determined by the fluorescence method. The experimental process indicates that it is feasible to use terahertz metamaterials to detect the reaction process of organic matter.