Super high quality Si crystal technology

Group1-1 Super high quality Si crystal technology

1. Objectives

The development of an innovative method which enables to grow high-quality Si ingots, and the supply of high-quality Si wafers for solar cells.

2. Methods

Basing on the “Noncontact Crucible method” developed by our laboratory, we develop innovative method realizing high-quality Si ingots.

3. Goal

• (1) Improvement of quality： dislocation-free, low oxygen concentration, low-content carbon, high-purity, quite-homogenous crystals
• (2) large-scaling of ingots, reducing the production cos

　

Fabrication process for silicon nanowire and characterization

Group2-1 Metal assisted etching and innovative process

1. Objectives

Development of silicon based nanowires with a bandgap of 1.7 eV and good optical confinement, and core technologies for nanowire solar cells.

2. Methods

• (1) Solid phase crystallization of amorphous silicon nanowires
  We realize Silicon nanowires with 4 nm diameter by solid phase crystallization of amorphous silicon nanowires which are fabricated by metal-assisted chemical etching using silica nanoparticle
• (2) Silicon-based superlattice nanowire solar cells
  We develop silicon-based superlattice nanowires with diameters less than 1μm. The nanowire structure enhances the optical confinement of the bandgap controlled superlattices
• (3) Amorphous silicon nanowire solar cells
  We develop high efficiency amorphous silicon (bandgap : 1.7 eV) solar cell by combining thin-film silicon solar cell technologies and nanowire technologies.

3. Goal

• (1) Development of silicon nanowires with 4 nm diameter
• (2) Development of silicon-based superlattice nanowires with diameters less than 1μm
• (3) Realization of high efficiency amorphous silicon solar cells.

Group2-2 Self Organization

1. Objectives

Fabrication of silicon nano-wires using bionano template and application to heterostructure solar cells

2. Methods

• (1) Fabricate silicon nano-wires on silicon substrates by bionano process using ferritin molecules
• (2) Characterize silicon nano-wires in the viewpoint of optoelectronic properties
• (3) Make heterostructure of silicon nano-wires and silicon substrates

3. Goal

• (1) Development of technologies fablicationg silicon mano-wires (5 – 10 nm diameter) on silicon substrates
• (2) Application to high efficiency silicon solar cells in heterostructures with nanowires

Group2-3 Fabrication of Nanowire Thin Films

1. Objectives

Realization of fundamental structure of Si nanowire thin film solar cell by combining novel fabrication technology of Si nanowires and wafer-equivalent crystalline Si thin films

2. Methods

• (1) Develop a novel fabrication technology of Si nanowires embedded in a dielectric matrix
• (2) Develop crystal growth process of wafer-equivalent of crystalline Si thin films on large-area low-cost substrates based on metal-induced layer exchange process

3. Goal

• (1) Development of novel fabrication technology of Si nanowires
• (2) Realization of high-quality crystalline Si thin films with controlled crystal orientations and large crystal grains

Nano-Wire Solar Cells

Group3-1 High efficiency Si solar cells

1. Objectives

Realization of nano-wire/silicon tandem solar cells

2. Methods

• (1) Develop a new heterojunction solar cells using nanocrystalline 3C-SiC or microcrystalline SiO as hetero-emitter
• (2) We study process technologies to fabricate striped nanowalls with a width of several nm, passivation method for the surface of nanowalls, and electrode formation and interconnection method for output current
• (3) Develop basic technology such as junction-formation, surface-passivation, and contact-formation on silicon microwire structure

3. Goal

• (1) Make samples of tandem solar cells in which a nano-wire solar cell and Si heterojunction solar cell are stacked in a monolithic or mechanical manner and demonstrate 30% conversion efficiency
• (2) Fabricate test samples by applying state-of-art process technologies developed for ULSI
• (3) Development of basic technology such as junction-formation, surface-passivation, and contact-formation on silicon microwire structure including technology for appropriate evaluation of each item, and application of these technologies for nanowire structure

Group3-2 Coupling structure

1. Objectives

Investigation of optical and electrical coupling technique between top cell and bottom cell in the high efficiency nanowire silicon/ hetero junction silicon tandem solar cells

2. Methods

Develop techniques to fabricate optical coupling layer consist mainly of transparent conductive oxide layer to develop these coupling structures

3. Goal

• (1) Development of techniques to decrease optical and electrical loss at the interface of the top nanowire silicon cell and bottom hetero junction silicon cell
• (2) Development of surface treatment method of transparent conductive oxide layer to fabricate nanowire silicon directly from the surface, which will decrease defects on the growth interface of nanowire silicon

Group3-3 Optical-Confinement and Device-Fabrication techniques

1. Objectives

Development of Si-nanowire solar cell which has a wide band-gap in order to utilize short-wavelength light more

2. Methods

• Develop the optical-confinement and the cell-fabrication techniques on Si nanowire solar cell

3. Goal

• (1) Development of TCO(Transparent Conductive Oxide) material, multi-layer structure and texture shape, which achieve high trasparency and high light scattering in the light incidence side
• (2) Development of p-n junction, passivation and back electrode processes in order to achieve high performance Si-nanowire solar cell