应用于CdTe太阳能电池热离子发射与扩散理论

该文运用了载流子的热离子发射理论与扩散理论来分析类型II异质结CdTe薄膜太能电池的载流子输运过程,得到了一个综合而全面的载流子电流电压输运方程;由该输运方程可知,对于窄准中性区的CdTe太能电池,流过其结的总电流由热离子发射过程来制约;反之,则由扩散过程来限制结的总电流。对于基于类型II异质结的薄膜太阳能电池,该输运方程可以为其更深入的研究,如各类掺杂情况边界条件的确定、转换效率的计算等,提供很好的理论基础。     

Thermoelectric transport in graphene and 2D layered materials

ABSTRACT

In early 90s, Hicks and Dresselhaus proposed that low dimensional materials are advantages for thermoelectric applications due to the sharp features in their density-of-states, resulting in a high Seebeck coefficient and, potentially, in a high thermoelectric power factor. Two-dimensional (2D) materials are the latest class of low dimensional materials studied for thermoelectric applications. The experimental exfoliation of graphene, a single-layer of carbon atoms in 2004, triggered an avalanche of studies devoted to 2D materials in view of electronic, thermal, and optical applications. One can mix and match and stack 2D layers to form van der Waals hetero-structures. Such structures have extreme anisotropic transport properties. Both in-plane and cross-plane thermoelectric transport in these structures are of interest. In this short review article, we first review the progress achieved so far in the study of thermoelectric transport properties of graphene, the most widely studied 2D material, as a representative of interesting in-plane thermoelectric properties. Then, we turn our attention to the layered materials, in their cross-plane direction, highlighting their role as potential structures for solid-state thermionic power generators and coolers.     

Diffusion emission model for solid-state photon-enhanced thermionic emission solar energy converters

Solid-state photon-enhanced thermionic emission (PETE) solar energy converters are new devices that can directly convert solar energy into electrical power at elevated temperatures. This study proposes a new solid-state PETE device structure with a p-type doped semiconductor as the absorber. A model based on a 1D steady-state continuity equation is presented to simulate the diffusion and emission of photogenerated carriers and to calculate the efficiencies. This model can evaluate the effect of device structure and material parameters on performance and efficiency. Calculation results show that the new device is more efficient compared with the original device. A longer electron diffusion length is favourable for enhancing efficiency. Moreover, the optimal absorber thickness is predicted. Our analyses also show that the front interface strongly affects conversion efficiency, which emphasises the need to reduce interface recombination losses. The results of this study may serve as bases for the optimum design of practical solid-state PETE devices.     

Study of schottky barrier heights of indium-tin-oxide on p-GaN using x-ray photoelectron spectroscopy and current-voltage measurements

In this study, the current density-voltage (J-V) characteristic of Schottky diodes of indium-tin-oxide (ITO) contacts to p-type GaN (p-GaN) has been investigated. The calculated barrier-height value of ITO/p-GaN samples using the thermionic field-emission (TFE) model is 3.2 eV, which implies that the work function of ITO is equal to 4.3 eV. The result is supported by J-V measurements of ITO/n-type GaN Schottky diodes. On the other hand, the barrier height of ITO/p-GaN was also determined from x-ray photoelectron spectroscopy (XPS) data. The analysis of the XPS spectral shifts indicated that this observed barrier-height value of ITO/p-GaN by XPS is in good agreement with the value of 3.2 eV obtained from J-V measurements.     

Extension of thermophysical and thermodynamic property measurements by laser pulse heating up to 10,000 K. II. Under vacuum

The experimental and theoretical efforts for the extension of thermodynamic property measurements up to 10,000 K by a transient-type dynamic laser pulse-heating technique under vacuum (LHV) are reviewed. The technique includes laser pulse heating, mass spectrometry, multiwavelength pyrometry, spectroscopy, high-speed photography, Langmuir probe, and high-tension diode studies. The experimental requirements and applicability limits of this transient technique at extreme rates of evaporation and charged particle emission under hydrodynamic flow conditions are discussed. Special attention is given to the study of the vaporization behavior and equation of state of multicomponent systems, the charged particle emission of ions and electrons, and the gas dynamic expansion mechanism of the evaporating jet. Further applications are the study of the reaction mechanism of combustion processes to investigate their efficiency and pollution.Paper presented at the First Workshop on Subsecond Thermophysics, June 20–21, 1988, Gaithersburg, Maryland, U.S.A.     

纳米钨粉及其稀土钨材料的制备新工艺研究

采用"液氮预冻-冷冻干燥-两段还原"获得了纳米钨粉,研究了纳米钨粉制备过程的物相组成和形貌,采用“液液掺杂-冷冻干燥-两段还原-SPS”制备了纳米Ce-W发射材料,研究了粉末和材料的形貌、铈的分布和高温扩散、以及材料的表面性能,并测量了材料热发射性能。     

VCSEL中布拉格反射体的电流机制和伏安特性

采用张弛法数值求解静电势的泊松方程 ,得出垂直腔面发射激光器 (VCSEL)中 N型和 P型分布布拉格反射体 (DBR)中一个周期单元的精确能带图。并以此为依据 ,从理论上分别分析和比较了多子漂移扩散、纯漂移和热电子发射电流机制所起的作用。指出由一对反对称同型异质结构成的 DBR一个周期单元总是表现出欧姆性 ,但热电子发射电流机制的存在容易使每个结呈现整流特性 ,以致在电流输运过程中起主要作用的是其反向特性 ,导致偏压和电阻过大器件不能正常工作。但是漂移扩散机制具有明显欧姆性 ,在利用缓变 DBR结构消除异质尖峰势垒之后漂移扩散机制将决定主要的电流输运     

THERMIONIC EMISSION OF Mo-Y_2O_3 FILAMENT CATHODE

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Unraveling Temperature‐Dependent Contact Electrification between Sliding‐Mode Triboelectric Pairs

The underlying mechanism on contact electrification (CE) has remained a topic of debate over centuries, and it is argued to be due to electron transfer, ion transfer, and/or even material species transfer. Recently, a previous study shows that CE is dominated by electrons, at least for solid–solid cases. Herein, by using a model detailing the charge transfer between triboelectric surfaces and thermionic emission of electrons via employing a sliding mode Ti–SiO₂ triboelectric nanogenerator (TENG), surface charge decay behavior is scrutinized in lateral‐sliding mode during operation at high temperature. The temperature dependence of TENG electric output contributes to characteristic metal–dielectric and dielectric–dielectric CEs, thereby providing further evidence that electrons are the dominating transferred charges in CE. The total surface charge output of the TENG is rationalized as a direct consequence of the coupling of the rate of electron thermionic emission, the charge transfer rate of CE, and the changing rate of the contacted area between the two materials. When the contacting area is larger than the displaced area, the CE between the two materials is the major contributor to measured surface charge. Conversely, the thermionic emission of the exposed surfaces dictates when the contacting area is smaller.