Cuibai Yang

Simulation of In0.65Ga0.35N single-junction solar cell

The performances of In0.65Ga0.35N single-junction solar cells with different structures, including various doping densities and thicknesses of each layer, have been simulated. It is found that the optimum efficiency of a In0.65Ga0.35N solar cell is 20.284% with 5 × 1017 cm−3 carrier concentration of the front and basic regions, a 130 nm thick p-layer and a 270 nm thick n-layer.

Theoretical design and performance of InxGa1?xN two-junction solar cells

The efficiencies of InxGa1-xN two-junction solar cells are calculated with various bandgap combinations of subcells under AM1.5 global, AM1.5 direct and AM0 spectra. The influence of top-cell thickness on efficiency has been studied and the performance of InxGa1-xN cells for the maximum light concentration of various spectra has been evaluated. Under one-sun irradiance, the optimum efficiency is 35.1% for the AM1.5 global spectrum, with a bandgap combination of top/bottom cells as 1.74 eV/1.15 eV. And the limiting efficiency is 40.9% for the highest light concentration of the AM1.5 global spectrum, with the top/bottom cell bandgap as 1.72 eV/1.12 eV.

Epitaxial growth and luminescence properties of ZnO-based heterojunction light-emitting diode on Si(1 1 1) substrate by pulsed-laser deposition

An epitaxial ZnO heterojunction light-emitting diode with an n-ZnO/MgO/TiN/n+-Si structure is produced by pulsed-laser deposition. By introducing a thin MgO/TiN buffer and a low temperature (LT) ZnO buffer, layer-by-layer growth of high quality ZnO epi-layer on Si(1 1 1) has been realized, which was confirmed by in situ reflection high-energy electron diffraction (RHEED), transmission electron microscopy, high-resolution x-ray diffraction, resonant Raman spectra and photoluminescence spectroscopy. Combining in situ RHEED with Phi-scan XRD analysis, the in-plane epitaxial growth of ZnO[1 1 0]||MgO[1 0 ]||Si[1 0 ] has been demonstrated. The strong room temperature electroluminescence (EL) with a broad emission band ranging from 1.46 to 3.5 eV and centred at 2.31 eV could be observed from the diode under relative low injection current. Furthermore, the EL output light intensity is enhanced obviously by improving the ZnO crystal quality via inserting a ZnO LT buffer layer.

InGaN/GaN multiple quantum well solar cells with an enhanced open-circuit voltage

In this paper, InGaN/GaN multiple quantum well solar cells (MQWSCs) with an In content of 0.15 are fabricated and studied. The short-circuit density, fill factor and open-circuit voltage (Voc) of the device are 0.7 mA/cm2, 0.40 and 2.22 V, respectively. The results exhibit a significant enhancement of Voc compared with those of InGaN-based hetero and homojunction cells. This enhancement indicates that the InGaN/GaN MQWSC offers an effective way for increasing Voc of an In-rich InxGa1−xN solar cell. The device exhibits an external quantum efficiency (EQE) of 36% (7%) at 388 nm (430 nm). The photovoltaic performance of the device can be improved by optimizing the structure of the InGaN/GaN multiple quantum well.

Influence of electric field on persistent photoconductivity in unintentionally doped n-type GaN

The influence of electric field on persistent photoconductivity in unintentionally doped n-GaN is investigated. It was found that under higher electric field the build-up course was slowed down while the decay course was accelerated. After a higher-voltage pulse, it was observed that the current dropped to a value lower than the dark current, and a current increase that lasted for thousands of seconds was observed. It is suggested that the above phenomena should be caused by the increase in capture rate of electron traps with electric field and are related to the Coulomb-repulsive characteristic of defects related to persistent photoconductivity.

Spin reorientation and magnetohistory of DyFe12-xNbx compounds

Structural and magnetic properties, especially the magnetocrystalline anisotropy of DyFe12-xNbx compounds with x = 0.55-0.85, have been investigated. The easy magnetization directions at room temperature for all the compounds are along the c-axis. With decreasing temperature the magnetocrystalline anisotropy changes from easy axis to easy cone at Tsr2, then to easy plane at Tsr1. A spin phase diagram has been constructed for DyFe12-xNbx. The change of magnetocrystalline anisotropy was further investigated by the angular dependence of magnetization with respect to the magnetic field at various temperatures. The temperature dependence of the cone angle was determined for DyFe11.3Nb0.7. It is noteworthy that with increasing Nb content both Tsr1 and Tsr2 decrease monotonically while the Curie temperature is almost independent of Nb content. The cone angle increases monotonically with decreasing temperature from Tsr2 and discontinuously comes up to 90° at Tsr1. The temperature dependence of the cone angle can be quite well defined in terms of crystal field theory. In addition, an obvious magnetohistory effect was observed for all compounds at low temperature. The critical field of magnetohistory was found to be smaller than 0.5 T for DyFe11.3Nb0.7.

GaInNAs/Ge (1.10/0.67 eV) double-junction solar cell grown by metalorganic chemical vapor deposition for high efficiency four-junction solar cell application

GaInNAs materials with narrow bandgaps of 1.10 eV have been grown on a Ge substrate by metalorganic chemical vapor deposition to fabricate GaInNAs/Ge (1.10/0.67 eV) double-junction solar cells. We have studied the photovoltaic characteristics and the external quantum efficiencies of the double-junction cells with various annealing conditions and different GaInNAs base layer thicknesses. The best external quantum efficiency is obtained from the double-junction cell with a 1170 nm thick GaInNAs base layer annealed at 675 °C for 30 min. Under AM1.5G illumination, the best double-junction cell has a short circuit current density (J SC) as 23.63 mA cm−2, which is dominated by the J SC of the GaInNAs subcell.

Hydrogen sensors based on Pt-AlGaN/AIN/GaN Schottky diode

Pt/AlGaN/AlN/GaN Schottky diodes have been fabricated and characterized for H2 sensing. Platinum (Pt) with a thickness of 20nm was evaporated on the sample to form the Schottky contact. The ohmic contact, formed by evaporated Ti/Al/Ni/Au metals, was subsequently annealed by a rapid thermal treatment at 860°C for 30 s in N2 ambience. Both the forward and reverse current of the device increased greatly when exposed to H2 gas. The sensors responses under different hydrogen concentrations from 500ppm to 10% H2 in N2 at 300K were investigated. A shift of 0.45V at 297K is obtained at a fixed forward current for switching from N2 to 10% H2 in N2. Time response of the sensor at a fixed bias of 0.5 V was also measured. The turn-on response of the device was rapid, while the recovery of the sensor at N2 atmosphere was rather slow. But it recovered quickly when the device was exposed to the air. The decrease in the barrier height of the diode was calculated to be about 160meV upon introduction of 10% H2 into the ambient. The sensitivity of the sensor is also calculated. Some thermodynamics analyses have been done according to the Langmuir isotherm equation.

Magnetocrystalline anisotropy and exchange interaction in YCo12-xTix compounds

Magnetic and structural properties of YCo12-xTix compounds have been investigated by x-ray diffraction and magnetic measurements. X-ray diffraction patterns of aligned powder samples indicate that the easy magnetization direction at room temperature is along the c-axis for all the compounds. The lattice parameters increase monotonously while Curie temperature TC decreases with increasing Ti content. It was found that all the compounds investigated are strong ferromagnets by analysis of magnetic moments using a magnetic valence model. The values of anisotropy fields Ba at room temperature and 1.5 K decrease with increasing x. The easy-axis anisotropy of the YCo12-xTix compounds is mainly contributed by the Co atoms at 8i sites according to the individual-site-anisotropy model.

The design and research of distributed cooling type high concentrated photovoltaic module

At present, the conversion efficiency of high concentrated photovoltaic modules is about 30%, most of the solar energy is converted into heat, which will result in solar cell temperature rise and subsequent module efficiency decrease. For existing module with large solar cell, the heat source is concentrated and additional cooling fins must be used, resulting in high system complexity and cost rise. In order to lower the cost of photovoltaic, we developed distributed cooling type module with simple structure. This paper depicts a distributed cooling design for high concentrated photovoltaic module, as well as the thermal simulation of this design with analysis software. Module prototype was also made to test the actual effect. The final outdoor results showed high consistency with the simulation results. The chip temperature can be lower than 45℃ and the module outdoor working efficiency is higher than 26% ，and lower temperature provide a guarantee of long-term reliability to module packaging material.