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Crystallization of Silicon for Solar Cell Applications

IP.com Disclosure Number: IPCOM000087819D
Original Publication Date: 1977-Mar-01
Included in the Prior Art Database: 2005-Mar-03
Document File: 2 page(s) / 36K

Publishing Venue

IBM

Related People

Von Gutfeld, RJ: AUTHOR

Abstract

When solar cells are made using amorphous silicon (Si) films, these films are converted to a useful crystalline size by laser-melting of small spots. Laser-melting converts local areas of the Si film by rapid heating and quenching without damaging the underlying substrate substantially. The laser beam is moved relative to the Si film or the film is moved relative to the beam at a predetermined fixed rate in order to crystallize narrow stripes of material by an effective zone melting and freezing process. This technique has disadvantages, such as the expense of the laser installation, small area conversion to crystalline Si, and extremely poor conversion of electrical energy into the laser-to-thermal energy in the Si film.

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Crystallization of Silicon for Solar Cell Applications

When solar cells are made using amorphous silicon (Si) films, these films are converted to a useful crystalline size by laser-melting of small spots. Laser- melting converts local areas of the Si film by rapid heating and quenching without damaging the underlying substrate substantially. The laser beam is moved relative to the Si film or the film is moved relative to the beam at a predetermined fixed rate in order to crystallize narrow stripes of material by an effective zone melting and freezing process. This technique has disadvantages, such as the expense of the laser installation, small area conversion to crystalline Si, and extremely poor conversion of electrical energy into the laser-to-thermal energy in the Si film.

In order to overcome these disadvantages, the present technique uses radiant heating from a hot filament ribbon to give efficient thermal coupling to the amorphous Si film. It is estimated that the blackbody wavelength maximum for a temperature of 3500 degrees K is approximately one micron. At this temperature, the radiant power from a tungsten filament ribbon is approximately 800W/cm/2/. The power couples efficiently into the amorphous Si film because
(1) the absorption constant of the film is large at this wavelength and (2) the width of the ribbon is made such as to produce essentially one dimensional heat flow, unlike that of a standard wire filament. If thermal diffusivity of the amorp...