Formation of solar cell-selective emitter using implant and anneal method

Abstract

A method of forming a solar cell, the method comprising: providing a semiconducting wafer having a pre-doped region; performing a first ion implantation of a dopant into the semiconducting wafer to form a first doped region over the pre-doped region, wherein the first ion implantation has a concentration-versus-depth profile; and performing a second ion implantation of a dopant into the semiconducting wafer to form a second doped region over the pre-doped region, wherein the second ion implantation has a concentration-versus-depth profile different from that of the first ion implantation, wherein at least one of the first doped region and the second doped region is configured to generate electron-hole pairs upon receiving light, and wherein the first and second ion implantations are performed independently of one another.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS[0001]This application claims priority to co-pending U.S. Provisional Application Ser. No. 61 / 131,687, filed Jun. 11, 2008, entitled “SOLAR CELL FABRICATION USING IMPLANTATION,” co-pending U.S. Provisional Application Ser. No. 61 / 131,688, filed Jun. 11, 2008, entitled “APPLICATIONS SPECIFIC IMPLANT SYSTEM FOR USE IN SOLAR CELL FABRICATIONS,” co-pending U.S. Provisional Application Ser. No. 61 / 131,698, filed Jun. 11, 2008, entitled “FORMATION OF SOLAR CELL-SELECTIVE EMITTER USING IMPLANTATION AND ANNEAL METHODS,” co-pending U.S. Provisional Application Ser. No. 61 / 133,028, filed Jun. 24, 2008, entitled “SOLAR CELL FABRICATION WITH FACETING AND IMPLANTATION,” and co-pending U.S. Provisional Application Ser. No. 61 / 210,545, filed Mar. 20, 2009, entitled “ADVANCED HIGH EFFICIENCY CRYSTALLINE SOLAR CELL FABRICATIONS METHOD,” which are all hereby incorporated by reference as if set forth herein.FIELD OF THE INVENTION[0002]The present invention relate...

AI Technical Summary

Benefits of technology

The present invention provides methods for improving the performance of solar cells by addressing the various ohmic losses arising from the use of older processes of doping solar substrates. These methods involve modifying the resistance of the substrate, contacts, busbars, and fingers, as well as the backside metallization. The invention also allows for the formation of a selective emitter and appropriate resistivity for the formation of contacts on the surface. The use of ion implantation and annealing systems can further enhance the atomic profile within the substrate. Overall, the invention provides a simple, effective, and inexpensive means for improving the efficiency of solar cells.

Problems solved by technology

The use of diffusion of dopant from the surface into the substrate is plagued by problems.

One of the main problems is the accumulation of unactivated dopants near the surface as the dopants are driven into the bulk of the material, which can vary the resistivity at different depths and regions of the substrate and thus lead to varying light absorption and electron-hole generation performance.

In particular, one problem encountered is the lack of utilization of the blue light as the result of formation of the so-called “dead layer.”

Additionally, lateral positioning of the dopants across the substrate is especially difficult as the line widths and wafer thicknesses are getting smaller.

Such placement can be very difficult for the present methodology of diffusion and screen printing.

Moreover, as wafers get thinner, from 150-200 microns of today down to less than 20 microns, vertical and batch diffusion and screen printing becomes extremely difficult or even impossible.

Furthermore, the use of diffusion has been unable to provide the ideal levels of dopant concentration and resulting resistivity.

Diffusion is unable to address each region separately and is limited to a sheet resistance of about 50 Ohms / square (Ω / □) for both regions, which is not quite high enough for the electron-hole pair generation region and not quite low enough for the contact region.

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