Hideyuki Yagi

Bifacial multicrystalline silicon solar cells

A bifacial solar cell structure is applied to multicrystalline substrates obtained from the OTC cast material. The double sided cathode configuration made it possible to collect photogenerated minority carriers from the nearest side of the cell, which allows the minority carrier not necessarily to travel across the substrate having short diffusion lengths. The rear cathode acts as a current booster for the front cathode for light entering from the front side, and vice versa. Because of this two fold current enhancement, cell outputs equivalent to nearly 20% efficiency are obtainable from a 15% cell when 30% albedo from the rear side is incorporated. A simplified screen printing process for cell fabrication provides a promising method of scaled production.<<ETX>>

Highly efficient, large-area polycrystalline silicon solar cells fabricated using hydrogen passivation technology

Highly efficient, large area polycrystalline silicon solar cells have been fabricated using ion implantation as a hydrogen passivation technique. A new high-current ion implanter with a bucket-type ion source has been developed to hydrogenate crystal defects in cast polycrystalline cells. Effective hydrogen passivation of the defects has been realized by implanting hydrogen ions into cast cells from the back surfaces and increasing the hydrogen ion energy and dose. A scanning light beam-induced current image of the polycrystalline cells shows that lowering of the induced current distribution at linear grain boundaries is almost completely eliminated, but not at irregular grain boundaries. The resultant polycrystalline cells exhibit a high conversion efficiency of 15.2% for a large area of 100 cm2.

Electrical Conduction of Silicon Nitride Films Deposited by SiH4-NH3 Reaction

The electrical conduction of silicon nitride films deposited pyrolytically on silicon substrates by the reaction of silane (SiH4) and ammonia (NH3) is caused by the Pool-Frenkel mechansim at room temperature and by the tunnel mechanism at a temperature of 208 K. When the deposition temperature is 850°C, the electrical conductivity of the films at room temperature and 208 K decreases with increasing NH3/SiH4 ratio. When the NH3/SiH4 ratio is 30, the electrical conductivity of the films at room temperature and 208K is the lowest value at a deposition temperature 90O°C and 850°C, respectively.

Electrical and Mechanical Properties of Silicon Nitride Films Deposited by the SiCl4-NH3 Reaction

Both the electrical conductivity of silicon nitride films at room temperature and the radius of curvature of a silicon wafer with a silicon nitride film are fairly independent of the deposition temperature and NH3/SiCl4 ratio during silicon nitride deposition. When a certain amount of hydrogen is added to the nitrogen carrier gas, the electrical conductivity decreases. The radius of curvature of a wafer with a film deposited by the SiCl4-NH3 reaction is smaller than that of a wafer with a film deposited by the SiH4-NH3 reaction.

Hydrogen passivation of large-area polycrystalline silicon solar cells by high-current ion implantation

The fabrication of highly efficient, large-area polycrystalline silicon solar cells using ion implantation as a hydrogen passivation technique is presented. The development of a high-current ion implanter with a bucket-type ion source to hydrogenate crystal defects in cast polycrystalline cells is also presented. Effective hydrogen passivation of the defects is realized by implanting hydrogen ions into the back surface of the cells and increasing the hydrogen ion energy and dose. The results show that the polycrystalline cells exhibit a high conversion efficiency of 15.2% for a large area of 100 cm/sup 2/.<<ETX>>

Cracks in Silicon Dioxide-Phosphosilicate Glass-Silicon Nitride Composite Layer on Silicon Substrates

Cracks occur more easily in the silicon dioxide (SiO2)-phosphosilicate glass (PSG)-silicon nitride (Si3N4) composite layer on silicon substrates than in the SiO2–Si3N4 composite layer. The Si3N4 limit thickness with respect to crack occurrence in the SiO2–PSG–Si3N4 composite layer decreases with increasing PSG film thickness within the range of 0–1500 A, with increasing P2O5 concentration in PSG film within the range of 0–10 mol% and with increasing Si3N4 deposition temperature. The local reaction of Si3N4 with P2O5 is probably the reason for crack occurrence in the SiO2–PSG–Si3N4 composite layer.