Han Peide

Optimization of the emitter region and the metal grid of a concentrator silicon solar cell

The optimizations of the emitter region and the metal grid of a concentrator silicon solar cell are illustrated. The optimizations are done under 1 sun, 100 suns and 200 suns using the 2D numerical simulation tool TCAD software. The optimum finger spacing and its range decrease with the increase in sheet resistance and concentration ratio. The processes of the diffusion and oxidization in the manufacture flow of the silicon solar cells were simulated to get a series of typical emitter dopant profiles to optimize. The efficiency of the solar cell under 100 suns and 200 suns increased with the decrease in diffusion temperature and the increase in oxidation temperature and time when the diffusion temperature is lower than or equal to 865 °C. The effect of sheet resistance of the emitter on series resistance and the conversion efficiency of the solar cell under concentration was discussed.

Optical properties in 1D photonic crystal structure using Si/C60 multilayers

The feasibility of using Si/C60 multilayer films as one-dimensional (1D) photonic band gap crystals was investigated by theoretical calculations using a transfer matrix method (TMM). The response has been studied both within and out of the periodic plane of Si/C60 multilayers. It is found that Si/C60 multilayer films show incomplete photonic band gap (PBG) behavior in the visible frequency range. The fabricated Si/C60 multilayers with two pairs of 70 nm C60 and 30 nm Si layers exhibit a PBG at central wavelength of about 600 nm, and the highest reflectivity can reach 99%. As a consequence, this photonic crystal may be important for fabricating a photonic crystal with an incomplete band gap in the visible frequency range.

First-Principles Study on the Stabilities of the Intermetallic Compounds in Mg-Nd Alloys

Abstract Using the first-principle pseudopotential plane wave (PPW) method based on the density functional theory, structural optimization was conducted on various intermetallic compounds of the binary Mg-Nd alloy. With their ground-state energies obtained, the structural stabilities of these intermetallic compounds were studied in terms of formation heat and binding energy of the alloy. The results show that the absolute values of the binding energies of various intermetallic compounds increase with the increase of Nd content, among which the absolute value of the binding energy of MgNd is the greatest while that of Mg 12 Nd is the smallest. It is indicated that among all the intermetallic compounds formed in Mg-Nd, the structure of MgNd is the most stable while that of Mg 12 Nd is the most unstable. This result is consistent with the experiment data. The Mg 12 Nd phase does not exist in the phase diagram of Mg-Nd alloy. In addition, the densities of electronic state of these structures were calculated and an explanation was given in terms of the electronic structure.

Boron implanted emitter for n-type silicon solar cell

The effects of ion doses on the properties of boron implanted Si for n-type solar cell application were investigated with doses ranging from 5× 1014 cm− 2 to 2× 1015 cm− 2 and a subsequent two-step annealing process in a tube furnace. With the help of the TCAD process simulation tool, knowledge on diffusion kinetics of dopants and damage evolution was obtained by fitting SIMS measured boron profiles. Due to insufficient elimination of the residual damage, the implanted emitter was found to have a higher saturation current density (J0e) and a poorer crystallographic quality. Consistent with this observation, Voc, Jsc, and the efficiency of the all-implanted p+–n–n+ solar cells followed a decreasing trend with an increase of the implantation dose. The obtained maximum efficiency was 19.59% at a low dose of 5× 1014 cm− 2. The main efficiency loss under high doses came not only from increased recombination of carriers in the space charge region revealed by double-diode parameters of dark I–V curves, but also from the degraded minority carrier diffusion length in the emitter and base evidenced by IQE data. These experimental results indicated that clusters and dislocation loops had appeared at high implantation doses, which acted as effective recombination centers for photogenerated carriers.

Effect of Cr, Mo, and Nb additions on intergranular cohesion of ferritic stainless steel: First-principles determination

Effects of Cr, Mo, and Nb on the ferritic stainless steel Σ(210) grain boundary and intragranularity are investigated using the first-principles principle. Different positions of solute atoms are considered. Structural stability is lowered by Cr doping and enhanced by Mo and Nb doping. A ranking on the effect of solute atoms enhancing the cohesive strength of the grain boundary, from the strongest to the weakest is Cr, Mo, and Nb. Cr clearly prefers to locate in the intragranular region of Fe rather than in the grain boundary, while Mo and Nb tend to segregate to the grain boundary. Solute Mo and Nb atoms possess a strong driving force for segregation to the grain boundary from the intragranular region, which increases the grain boundary embrittlement. For Mo- and Nb-doped systems, a remarkable quantity of electrons accumulate in the region close to Mo (Nb). Therefore, the bond strength may increase. With Cr, Mo, and Nb additions, an anti-parallel island is formed around the center of the grain boundary.

FIRST-PRINCIPLES STUDY OF STACKING FAULT ENERGY AND DEFORMATION TWIN\par ENERGY IN Al-Mg ALLOYS

By using first-principles method based on the density functional theory(DFT), the stacking fault energy(SFE)and deformation twin energy(DTE)for the(111)[112]slip system of pure Al metal and Al-Mg alloys were investigated.The dependence of these SFE and DTE on solid-solution Mg content and its accupation were specifically analyzed.Two major approximations were made in the process of calculation,which were local density approximation(LDA)and generalized gradient approximation(GGA-PW91),respectively.The calculated SFE values by using GGA-PW91 exhibit an excellent agreement with corresponding experimental measurements.For pure Al metal,the calculated SFE values are greater than those of DTE.Moreover,it is found that under the same deformation conditions,the DTE in pure Al and Al-Mg alloys increase monotonically with the increase of deformation twin thickness.In addition,the calculated results shows that 6-layer twin possesses the lowest DTE,which is probably due to its mirror symmetry structure.Also noteworthy, our calculations reveal a noticeable decreased tendency of SFE and DTE with Mg content increasing,while Mg occupying on stacking fault and twin boundary most likely increases SFE and DTE.There are no considerably detected effects of Mg atomic occupancy variation in Al-Mg alloy on its cohesive energy and formation energy.

First-principles study of the effects of selected interstitial atoms on the generalized stacking fault energies, strength, and ductility of Ni

We analyze the influences of interstitial atoms on the generalized stacking fault energy (GSFE), strength, and ductility of Ni by first-principles calculations. Surface energies and GSFE curves are calculated for the 〈11〉 (111) and 〈10〉 (111) systems. Because of the anisotropy of the single crystal, the addition of interstitials tends to promote the strength of Ni by slipping along the 〈10〉 direction while facilitating plastic deformation by slipping along the 〈11〉 direction. There is a different impact on the mechanical behavior of Ni when the interstitials are located in the slip plane. The evaluation of the Rice criterion reveals that the addition of the interstitials H and O increases the brittleness in Ni and promotes the probability of cleavage fracture, while the addition of S and N tends to increase the ductility. Besides, P, H, and S have a negligible effect on the deformation tendency in Ni, while the tendency of partial dislocation is more prominent with the addition of N and O. The addition of interstitial atoms tends to increase the high-energy barrier γmax, thereby the second partial resulting from the dislocation tends to reside and move on to the next layer.

Tensile properties of phase interfaces in Mg—Li alloy: A first principles study

Employing density functional theory, we study the tensile and fracture processes of the phase interfaces in Mg—Li binary alloy. The simulation presents the strain—stress relationships, the ideal tensile strengths, and the fracture processes of three phase interfaces. The results show that the α/α and α/β interfaces have larger tensile strength than that of β/β interface. The fractures of both α/α and β/β interfaces are ductile fractures, while the α/β fractures abruptly._Further analyses show that the fracture of the α/β occurs at the interface.