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Browse Prior Art Database

METHOD OF FABRICATING VERTICAL MULTIJUNCTION SOLAR CELLS

IP.com Disclosure Number: IPCOM000005458D
Original Publication Date: 1982-Jan-01
Included in the Prior Art Database: 2001-Oct-10
Document File: 2 page(s) / 98K

Publishing Venue

Motorola

Related People

Robert M. Handy: AUTHOR

Abstract

Vertical multijunction is desirable as means for improving the efficiency of solar cells. The carrier collecting p-n junctions are arranged to be perpendicular to the surface and closely spliced so that no matter where a light generated free carrier is created, it will always be close to a junction, preferably within adiffusion length, so that it can be collected before it recombines.

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@ MomROgA Techr+al Developments Volume 2

January 1982

METHOD OF FABRICATING VERTICAL MULTIJUNCTION

SOLAR CELLS

By Robert M. Handy

    Vertical multijunction is desirable as means for improving the efficiency of solar cells. The carrier collecting p-n junctions are arranged to be perpendicular to the surface and closely spliced so that no matter where a light generated free carrier is created, it will always be close to a junction, preferably within adiffusion length, so that it can be collected before it recombines.

   A typical structure is illustrated In Figure 1 which shows a cross-section of an n-type silicon wafer20 of thickness 21 in wnich are placed vertical p + regions 22, separated by n-regions 23 of width 24 and spacing 25. Light ray 26 is partly reflected (26r) at the surface and the balance absorbed within n-region 23 generating free carriers 27 which diffuse to junctions 28 or 29. Width 24 is preferably comparable to or less than a free carrier diffusion length, but in any case less than wafer thickness 21. Ohmic contact is made to the multiple n and p regions to connect them in series or in parallel by metallization means well known in the art. Despite their advantages for increased free carrier collection efficiency, vertical junc- tion solar cells are little used because they are difficult to construct. The present invention overcomes thisdifficulty.

   It is known that thermal gradients can cause impurity droplet migration in single crystal semicon- ductor materials such as silicon. The region left behind in the path of a migrating droplet is single crystal silicon doped to the solubility limit of the,impurity droplet material. These migration and doping effects take place at temperatures significantly below the melting point of pure silicon. This phenomena is described by W.G. Pfann in "Gradient Zone Melting," Journal of Metals, September, 1955, pp. 961-4.

   Figures 2A-C show how the effect can be used to provide vertical multijunctio...