# US 5,702,538 A · Silicon semiconductor wafer solar cell and process for producing said wafer

> Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt

- Number: US 5,702,538 A
- Document ID: US5702538A
- Status: Granted
- Kind: A
- Application number: 08/656,348
- Filed: 1996-06-14
- Granted: 1997-12-30
- Earliest claimed: 1993-12-17
- Assignees: Siemens Solar GmbH
- Inventors: Arthur Endros; Giuliano Martinelli
- Web page: https://patentgrep.com/patent/US5702538A

## CPC

- C30B 29/06: Silicon
- C30B 15/36: characterised by the seed, e.g. its crystallographic orientation
- H10F 10/14: Photovoltaic cells having only PN homojunction potential barriers
- H10F 71/121: {The active layers comprising only Group IV materials}
- H10F 77/16: Material structures, e.g. crystalline structures, film structures or crystal plane orientations
- Y02E 10/547: Monocrystalline silicon PV cells
- Y02P 70/50: Manufacturing or production processes characterised by the final manufactured product
- Y10S 117/902: Specified orientation, shape, crystallography, or size of seed or substrate
- Y10S 438/973: Substrate orientation
- C30B: SINGLE-CRYSTAL GROWTH (by using ultra-high pressure, e.g. for the formation of diamonds, B01J3/06); UNIDIRECTIONAL SOLIDIFICATION OF EUTECTIC MATERIAL OR UNIDIRECTIONAL DEMIXING OF EUTECTOID MATERIAL; REFINING BY ZONE-MELTING OF MATERIAL (zone-refining of metals or alloys C22B); PRODUCTION OF A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE (casting of metals, casting of other substances by the same processes or devices B22D; working of plastics B29; modifying the physical structure of metals or alloys C21D, C22F); SINGLE CRYSTALS OR HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE; AFTER-TREATMENT OF SINGLE CRYSTALS OR A HOMOGENEOUS POLYCRYSTALLINE MATERIAL WITH DEFINED STRUCTURE (for producing semiconductor devices or parts thereof H10); APPARATUS THEREFOR
- H10F: INORGANIC SEMICONDUCTOR DEVICES SENSITIVE TO INFRARED RADIATION, LIGHT, ELECTROMAGNETIC RADIATION OF SHORTER WAVELENGTH OR CORPUSCULAR RADIATION
- Y02E: REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02P: CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y10S: TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS

## Abstract

A silicon semiconductor wafer is constructed from three mutually inclined monocrystalline regions (6, 7, 8) which form three circular sectors of the wafer whose interfaces and boundary lines consequently extend radially with respect to one another and form angles (W6, W7, W8) of less than 180.degree. with one another. In this arrangement, two of the interfaces are first-order twin grain boundaries between two <111> crystal planes in each case. The silicon semiconductor wafer is used to produce inexpensive high-performance solar cells.

## Claims

### Claim 1

A solar cell comprising: a mechanically robust 60 .mu.m to 90 .mu.m thick silicon semiconductor wafer as a solar cell substrate, said wafer having a front side and a rear side, and said wafer having three mutually inclined monocrystalline regions which form three circular sectors whose interfaces and boundary lines extend radially with respect to one another and form angles of less than 180.degree. with one another, two of the interfaces being first-order twin grain boundaries between two <111> crystal planes in each case, the wafer being produced from crucible-drawn silicon;
a light p-doping in the wafer;
a shallow, n+-doped emitter 0.2 .mu.m to 2 .mu.m deep on the front side;
a first passivation layer on the front side, the first passivation layer being an oxide layer which produces a charge carrier recombination rate on the surface of said wafer of less than 1000 cm/s;
a second passivation layer or a back surface field on the rear side, the charge carrier recombination rate on the rear side being less than 100 cm/s; and
current-collecting contacts respectively on the front and rear sides.

### Claim 2 (depends on 1)

The solar cell as claimed in claim 1, wherein the solar cell has a conversion efficiency of at least 20 percent.

### Claim 3 (depends on 1)

The solar cell as claimed in claim 1, wherein the interfaces are approximately perpendicular to the plane of the wafer and form angles W6, W7, and W8 with respect to one another, where:
W7=W8=(360.degree.-W6)/2 and W6=109.47.degree..+-.2.degree..

### Claim 4 (depends on 1)

The solar cell as claimed in claim 1, wherein the surfaces of the three monocrystalline regions are <110> crystal planes.

### Claim 5 (depends on 1)

The solar cell as claimed in claim 1, wherein the solar cell has a texturing on the front side in the form of cones etched into a surface of the wafer.

### Claim 6

A process for producing a silicon semiconductor wafer for a solar cell substrate having three mutually inclined circular-sector-shaped monocrystalline regions, comprising the steps of:
producing three octahedral seed crystals by sawing the crystals out of a conventional <110>-oriented monocrystal such that all octahedral surfaces are identical with <111> crystal planes;
joining two of the seed crystals by laying the two seed crystals on top of one another and fixing the two seed crystals with a wire so that a first-order twin grain boundary is formed;
growing, utilizing the two joined seed crystals, a bicrystal using a crystal growing process;
sawing a wedge-shaped piece out of the bicrystal and in this process a <111> plane of the two half-crystals is laid bare in each case;
inserting the third seed crystal into the wedge-shaped gap such that a second first-order twin grain boundary is formed with the <111> crystal surface;
shortening the bicrystal to approximately a length of the third seed crystal to form a tricrystal seed;
pulling a tricrystal ingot from a silicon melt utilizing a crystal growing process using the tricrystal seed; and
sawing the semiconductor wafer out of the tricrystal ingot using a wire saw.

### Claim 7 (depends on 6)

The process as claimed in claim 6, wherein a molybdenum wire is used to fix the seed crystals.

### Claim 8 (depends on 6)

The process as claimed in claim 6, wherein a Czochralski process is used for crystal growing.

### Claim 9 (depends on 6)

The process as claimed in claim 6, wherein the tricrystal seed and the growing tricrystal ingot are aligned such that six mirror-like facets form on the tricrystal ingot.

### Claim 10 (depends on 6)

The process as claimed in claim 6, wherein after pulling a first tricrystal ingot from a quartz melting crucible, the silicon melt which is not more than half consumed is topped up by adding fresh silicon and the entire process is repeated up to ten times.

### Claim 11 (depends on 10)

The process as claimed in claim 10, wherein a sawn-off tip of a previously pulled tricrystal ingot is used as a seed crystal.