Ding Jianning

Analysis of the p+/p window layer of thin film solar cells by simulation

The application of a p+/p configuration in the window layer of hydrogenated amorphous silicon thin film solar cells is simulated and analyzed utilizing an AMPS-1D program. The differences between p+?p?i?n configuration solar cells and p?i?n configuration solar cells are pointed out. The effects of dopant concentration, thickness of p+-layer, contact barrier height and defect density on solar cells are analyzed. Our results indicate that solar cells with a p+?p?i?n configuration have a better performance. The open circuit voltage and short circuit current were improved by increasing the dopant concentration of the p+ layer and lowering the front contact barrier height. The defect density at the p/i interface which exceeds two orders of magnitude in the intrinsic layer will deteriorate the cell property.

Piezoelectric and Dielectric Properties of Dy2O3-Doped Bi0.5 (Na0.82K0.18)0.5TiO3 Lead-Free Ceramics

xDy2O3-Bi0.5(Na0.82K0.18)0.5TiO3(0-0.4wt%) ceramics were synthesized by conventional solid-state processes. X-ray diffraction pattern confirmed that the tetragonal and rhombohedral phases co-existed in the Dy2O3 doped Bi0.5(Na0.82K0.18)0.5TiO3 ceramics from x = 0.05 to 0.4 wt% Dy2O3. SEM images indicate that doping of Dy2O3 promotes the formation of the ceramics with homogenous microstructures and high density. The Bi0.5(Na0.82K0.18)0.5TiO3 ceramics remain a diffuse phase transition behavior after the addition of Dy2O3. The electrical properties of BNKT ceramics can be improved by adding suitable amount of Dy2O3, giving optimum value of 1765 (1 kHz) at x = 0.10, 152 pC/N and 32.5μC/cm2 at x = 0.15 respectively.

Dy2O3 Doped (Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 Ceramics

(Ba0.85Ca0.15)(Ti0.90Zr0.10)O3 (BCTZ)+ xwt%Dy2O3(x = 0–0.20) ceramics were prepared by conventional solid-state process, and the effects of Dy2O3 on the microstructure and the electrical properties were investigated. X-ray diffraction pattern confirmed that the BCTZ ceramics exhibit tetragonal structure, and stable solid solutions between BCTZ and Dy2O3 were well established in the range investigated. SEM images show that the addition of Dy2O3 restrains abnormal grain growth and leads to the formation of homogeneous microstructures during sintering. Dy3+ occupies B-site at x = 0–0.15, and A-site at x = 0.20 respectively. A-site occupation of Dy3+ into BCZT ceramic facilitates the ferroelectric domains reorientation and thus improves the piezoelectric properties significantly from 315pC/N(x = 0) to 425pC/N(x = 0.20). The corresponding planar electromechanical coupling factor at x = 0.20 was 49.1%. The A-site occupation(x = 0.2) also exhibits superiority to the improvement of dielectric properties and ferroelectric properties for BCZT ceramics (ϵ33 = 3264 at 1 kHz, 2Pr = 28.4μC/cm2, 2Ec = 5.28 kV/cm).

Microstructure and mechanical properties of heat-treated GeSb2Te4 thin films

The effect of annealing on microstructure, adhesive and frictional properties of GeSb2Te4 films were experimentally studied. The GeSb2Te4 films were prepared by radio frequency (RF) magnetron sputtering, and annealed at 200 °C and 340 °C under vacuum circumstance, respectively. The adhesion and friction experiments were mainly conducted with a lateral force microscope (LFM) for the GeSb2Te4 thin films before and after annealing. Their morphology and phase structure were analyzed by using atomic force microscopy (AFM) and X-ray Diffraction (XRD) techniques, and the nanoindention was employed to evaluate their hardness values. Moreover, an electric force microscope (EFM) was used to measure the surface potential. It is found that the deposited GeSb2Te4 thin film undergoes an amorphous-to-fcc and fcc-to-hex structure transition; the adhesion has a weaker dependence on the surface roughness, but a certain correlation with the surface potential of GeSb2Te4 thin films. And the friction behavior of GeSb2Te4 thin films follows their adhesion behavior under a lower applied load. However, such a relation is replaced by the mechanical behavior when the load is relatively higher. Moreover, the GeSb2Te4 thin film annealed at 340 °C presents a lubricative property.

Nano-structured red phosphorus/porous carbon as a superior anode for lithium and sodium-ion batteries

To enhance electrochemical performance of lithium or sodium-ion batteries (LIBs or NIBs), active materials are usually filled in porous conductive particles to produce anode composites. However, it is still challenging to achieve high performance anode composites with high specific capacity, excellent rate performance, high initial Coulombic efficiency (ICE) and long cycle life. Based on these requirements, we design and fabricate activated carbon-coated carbon nanotubes (AC@CNT) with hierarchical structures containing micro- and meso-pores. A new structure of phosphorus/carbon composite (P@AC@CNT) is prepared by confining red P in porous carbon through a vaporization-condensation-conversion method. The micro-pores are filled with P, while the meso-pores remain unoccupied, and the pore openings on the particle surface are sealed by P. Due to the unique structure of P@AC@CNT, it displays a high specific capacity of 1674 mA h g−1 at 0.2 C, ultrahigh ICE of 92.2%, excellent rate performance of 1116 mA h g−1 at 6 C, and significantly enhanced cycle stability for LIBs. The application of P@AC@CNT in NIBs is further explored. This method for the fabrication of the special composites with improved electrochemical performance can be extended to other energy storage applications.摘要为了提升锂离子或钠离子电池的电化学性能, 通常的做法是将活性材料填充到多孔导电颗粒中来形成复合材料. 然而, 同时实现电池的高容量、高倍率、高首次库仑效率和长循环寿命等性能仍是一项挑战. 针对这些需求, 我们设计并制备了具有分等级微中孔结构的活性炭包覆碳纳米管材料. 采用蒸发冷凝转化法制备了一种将红磷限制在碳材料孔隙中的新型磷/碳(P/C)复合材料. 在这种复合材料中,碳基的微孔被红磷充斥而介孔被保留. 材料颗粒表面的孔隙被红磷所堵塞. 由于所制备的P/C复合材料这种独特的结构, 其在锂离子电池中以0.2 C倍率充放电时展现了高达1674 mA h g−1的比容量和92.2%的首次库仑效率; 在6 C倍率充放时展现1116 mA h g−1的高容量和优秀的循环稳定性. 另外, 所制备的复合材料在钠离子电池中也展示了卓越的性能. 这种采用特殊结构来改善电化学性能的方法可推广到其他电池或储能应用中.

Composition Dependence of Electrocaloric Effect in (1 − x)Pb(Mg1/3Nb2/3)O3 −xPbTiO3 Single Crystals*

Composition dependence of electrocaloric effect is investigated in(1- x)Pb(Mg1/3Nb2/3)O3- xP b Ti O3 single crystals by using an eighth-order Landau–Devonshire theory. The applied electric field along [001] direction reduces the ferroelectric-ferroelectric phase transition temperatures, but increases the Curie temperatures. The electrocaloric coefficients of tetragonal phase are much larger than that of rhombohedral and monoclinic phase. A negative electrocaloric effect is observed near the MC-T phase transition in 0.69Pb(Mg1/3Nb2/3)O3-0.31 Pb Ti O3 single crystal. The application of a strong enough electric field results in a high adiabatic temperature change over a broad range of temperature.Therefore, it would be useful to construct a solid state cooling cycle over a broad temperature range for practical applications.

Effect of misfit strain on the electrocaloric effect of polydomain epitaxial ferroelectric thin films

The effect of misfit strain on the electrocaloric effect in polydomain epitaxial BaTiO3 thin films at room temperature is investigated using the Ginzburg—Landau—Devonshire thermodynamic theory. Numerical calculations indicate that the misfit strain has a large impact on the ferroelectric polarization states and the electrocaloric effect. Most importantly, the electrocaloric effect in the polydomain ca1/ca2/ca1/ca2 phase is much larger than that in the monodomain c phase and the other polydomain phases. Consequently, a large electrocaloric effect can be obtained by carefully controlling the misfit strain, which may provide potential applications in refrigeration devices.

Powder Preparation and Piezoelectric Properties Research of Bi0.5(Na0.82K0.18)0.5TiO3-BiFeO3 Lead Free Ceramics

(1-x)Bi0.5(Na0.82K0.18)0.5TiO3-xBiFeO3 (x = 0.01–0.07) lead-free piezoelectric ceramics were fabricated by citrate method. The influence of the BiFeO3 additive on the structure and electrical properties of the ceramics was investigated. XRD measurement confirmed that a single perovskite phase can be obtained in all the specimen sintered at 1120°C for 2 h, and the morphotropic phase boundary (MPB) with rhombohedral and tetragonal coexistence for the ceramics locates in range of x = 0–0.07. BiFeO3 doping (x = 0.03) improves densification of the specimen with relative density reaching up to 96.5%. Compared with Bi0.5(Na0.82K0.18)0.5TiO3, the specimen with BiFeO3 added gave an obvious increase of the dielectric constant and a remarkable increase of piezoelectric constant (135 pC N−1) at x = 0.03.

Photovoltaic properties of ferroelectric solar cells based on polycrystalline BiFeO

To study the ferroelectric photovoltaic effect based on polycrystalline films, preparation of high-quality polycrystalline films with low leakage and high remnant polarization is essential. Polycrystalline BiFeO3 (BFO) thin films with extremely large remnant polarization (2Pr = 180 C/cm2) were successfully deposited on glass substrates coated with indium tin oxide using a modified radio frequency magnetron sputtering method. Symmetric and asymmetric cells were constructed to investigate the ferroelectric photovoltaic effect in order to understand the relationship between polarization and photovoltaic response. All examined cells showed polarization-induced photovoltaic effect. Our findings also showed that the ferroelectric photovoltaic effect is highly dependent on the material used for the top electrode and the thickness of the polycrystalline film.研究意义铁酸铋 (BFO) 薄膜在铁电材料中具有较低的光学带隙和较高的剩余极化强度.因此,它在光伏方 面的应用受到广泛关注.多晶BFO薄膜一般以Pt作为底电极,本文利用射频磁控溅射的方法在ITO基底上制备 了高质量的BFO薄膜.这样的工艺具有大面积制备的可行性.基于高质量的BFO薄膜,本文继续探究了电极材 料、薄膜厚度和外电场极化对铁电光伏效应的影响,为拓宽铁电薄膜材料在光伏器件方面的应用提供了很好的 前提.创新要点成功利用常温磁控溅射和后期热退火 (500°C) 相结合的方法在ITO基底上制备了高质量的BFO薄膜, 其铁电性与以Pt作为缓冲层基底的薄膜相当甚至更加优越.室温下测得的剩余极化强度 (2Pr) 约为180 μC/cm2. 本文还系统地探究了电极材料、电极对称性、薄膜厚度以及外电场极化对铁电光伏效应的影响.所有的电池都 呈现出极化诱导的光伏效应.我们发现,使用氧化物电极 (ITO) 代替金属 (Ag) 电极,光电流增加明显;随 着膜厚的减小,光伏响应也明显增强.

Preparation of Bi3.15Dy0.85(Ti3-xFex)O12(x = 0-0.3) Ceramics and Their Electrical Properties

Bi3.15Dy0.85(Ti3-xFex)O12(x = 0−0.3) lead-free piezoelectric ceramics were prepared by a solid-state reaction method. The effects of the amount of Dy2O3 and Fe2O3 on the microstructure and electrical properties of the ceramics were investigated. X-ray diffraction shows that the introduction of Dy and Fe does not change the layered perovskite structure of Bi4Ti3O12. SEM images indicated that Bi3.15Dy0.85(Ti3-xFex)O12 ceramics with nearly pore-free microstructures and high densities were obtained. The dielectric constant decreases with the addition of Dy2O3, but remarkably increased with the amount of Fe2O3, and it decreases with frequency, showing a diffuse phase transition behavior.