Bin Ai

PC2D simulation and optimization of the selective emitter solar cells fabricated by screen printing phosphoric paste method

On the basis of perfect PC2D simulation to the measured current density vs voltage (J–V) curve of the best selective emitter (SE) solar cell fabricated by the CSG Company using the screen printing phosphoric paste method, we systematically investigated the effect of the parameters of gridline, base, selective emitter, back surface field (BSF) layer and surface recombination rate on performance of the SE solar cell. Among these parameters, we identified that the base minority carrier lifetime, the front and back surface recombination rate and the ratio of the sheet-resistance of heavily and lightly doped region are the four largest efficiency-affecting factors. If all the parameters have ideal values, the SE solar cell fabricated on a p-type monocrystalline silicon wafer can even obtain the efficiency of 20.45%. In addition, the simulation also shows that fine gridline combining dense gridline and increasing bus bar number while keeping the lower area ratio can offer the other ways to improve the efficiency.

Polycrystalline Silicon Films on SiO2 Substrate Treated by Excimer Laser Annealing

Selected area laser-annealed polycrystalline silicon (p-Si) thin films were prepared by a 248 nm excimer laser. 1 μm thick p-Si films with grain size less than 100 nm were deposited on SiO2 substrate by chemical vapor deposition using atmospheric pressure (APCVD). Grain sizes before and after annealing was examined by scanning electron microscopy (SEM) and the mechanism of grain growth was discussed in detail. The maximum grain size of a selected area laser-annealed p-Si film can be increased from 100 nm up to 2.9 μm on SiO2 substrate by using appropriate laser energy densities. It indicated that silicon grains in laser-annealed regions had grown up competitively with three stages.

Selected Crystallization of Different Thickness Amorphous Silicon by 248nm Wavelength Excimer Laser

Arrangement selected crystallization of different thickness from 100nm to 350nm of amorphous silicon thin films on glass were prepared by 248nm wavelength UV excimer laser. A cleverly designed 5-dot-mask was used to reshape the laser beam and the sample was placed and scanned by laser on a XY-Axis translation stage with the movement controlled by a programmable controller accurately in order to optimize the process conditions, different kinds of laser energies and thickness of amorphous silicon thin films were utilized. The laser-crystallized samples were characterized by Raman spectrometer, metallurgical microscope and scanning electron microscope (SEM). From the results we tend to draw the following conclusion that the poly-Si seed layer can gain better crystallization quality with higher laser pulse energy and thinner amorphous silicon thin films.

Epitaxial Growth of Silicon Films on SiO2 Patterned Si(100) Substrates by Atmospheric Pressure Chemical Vapor Deposition

In order to investigate the effect of selective area nucleation on epitaxial growth of silicon (Si) films, 35 µm thick Si films were deposited by atmospheric pressure chemical vapor deposition (APCVD) under the standard condition on two kinds of SiO2 patterned Si(100) wafers. One was circular patterns, and the other was striated patterns. Then, the structural properties of the as-deposited silicon thin films were investigated by metallurgical microscope, scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (TEM). The results show that normal epitaxial growth occurs on the exposed Si(100) regions, while just polycrystalline Si deposition happens on the SiO2 regions. Moreover, for the substrates with circular patterns, the as-deposited Si thin films possess pyramid surface morphology thus excellent light trapping performance being spontaneously formed, and the sizes of the pyramid grains approximately equal to the sum of the diameter and spacing of the round exposed Si regions.

APCVD Deposition of Si Film on SiO2 Patterned Si (111) Substrates for Solar Cells

We have investigated the deposition of silicon films on SiO2 patterned Si(111) substrates by atmospheric pressure chemical vapor deposition (APCVD) under standard condition. Oxidized silicon wafers with different sizes of circular and striated patterns were used as substrates for deposition of 35 μm silicon films. The influence of surface morphologies of substrates on epitaxial Si films has been discussed. The crystalline structures of the epitaxial Si films rely on the prepatterned substrates. Triangular prism-shaped grains have been obtained after depositing silicon film on substrates with circular patterns. While different size polycrystalline silicon grains appear on surfaces of Si films grown on SiO2 regions of substrates along the axis of striated patterns. Twins defects were observed in epitaxial Si films grown on SiO2 layers of the pretreated substrates.