Drive through doping process for manufacturing low back surface recombination solar cells

Claim 1

A method for passivating the back metallization of a solar cell and forming deep impurity doped regions under the back contacts of said solar cell, said method comprising the steps of: providing a p-type wafer of semiconductor material with a front and a back essentially parallel major surfaces; forming an n+ layer under the front major surface of said wafer defining an n + -p junction between the front and back major surfaces; forming a p+ layer under the back surface of said wafer defining a p + -p junction between the front and back major parallel surfaces, the p + -p junction and the n + -p junction defining a p-type layer therebetween; depositing a nonconductive layer on said major surface, said nonconductive layer having an exposed major surface essentially parallel to said back major surface; depositing a metal paste in a predetermined pattern onto the exposed major surface of said nonconductive layer; heating said wafer and said metal paste to a predetermined temperature so that said metal paste will oxidize, thus reducing the portion of said nonconductive layer located underneath said metal paste pattern, which remaining metal will continue melting into and alloying with portions of said p+ layer and portions of the p-type layer to a predetermined depth which is dependent on the temperature, time of heating and amount of metal paste used; and cooling said wafer to form p+ type impurity doped regions in a predetermined pattern extending from the back surface of said wafer into said wafer to a predetermined depth.

Claim 2

A method for passivating the back metallization of a solar cell and forming deep impurity doped regions under the back contacts of said solar cell, said method comprising the steps of: providing a p-type wafer of semiconductor material with a front and a back essentially parallel major surfaces; forming an n+ layer under the front major surface of said wafer defining an n + -p junction between the front and back major surfaces; forming a p+ layer under the back surface of said wafer defining a p + -p junction between the front and back major parallel surfaces, the p + -p junction and the n + -p junction defining a p-type layer therebetween; depositing a nonconductive layer on said major surface, said nonconductive layer having an exposed major surface essentially parallel to said back major surface; depositing a metal paste in a predetermined pattern onto the exposed major surface of said nonconductive layer; heating said wafer and said metal paste to a predetermined temperature so that said metal paste will oxidize, thus reducing the portion of said nonconductive layer located underneath said metal paste pattern, which remaining metal will continue melting into and alloying with portions of said p+ layer and portions of the p-type layer to a predetermined depth which is dependent on the temperature, time of heating and amount of metal paste used; and cooling said wafer to form p+ type impurity doped regions in a predetermined pattern extending from the back surface of said wafer into said wafer to a predetermined depth.

Claim 11

A method for passivating the back metallization of a solar cell and forming deep impurity doped regions under the back contacts of said solar cell, said method comprising the steps of: providing a p-type wafer of silicon with front and back major essentially parallel surfaces; forming an n + -p junction in said wafer under the front major surface, said junction being disposed between the front and back major surfaces and defining an n+ layer between said junction and the front major surface; maintaining said wafer at a predetermined temperature in the presence of a p-type impurity for a predetermined period of time to produce a p+ layer under said back surface, said p+ layer and said n+ layer defining a p-type layer therebetween; depositing a nonconductive layer upon said back major surface, said nonconductive layer having an exposed major surface essentially parallel to said back major surface; screen printing a metal paste in a predetermined pattern onto the exposed major surface of said nonconductive layer, said metal paste comprising fine metal particles suspended in a vehicle; heating said wafer and metal paste to a predetermined temperature so that said metal paste will oxidize, thus reducing the portion of said nonconductive layer located underneath said metal paste pattern, which remaining metal will continue melting into and alloying with portions of said p+ layer and with portions of said p-type layer to a predetermined depth which is dependent on the temperature and time, and amount of metal paste used; cooling said wafer to form p+ impurity doped regions that extend from at or near said back major surface of said wafer to a predetermined depth into said p-type layer; removing any excess metal and oxide layers formed during the above steps, leaving said nonconductive layer with openings therein extending from the exposed major surface of said nonconductive layer to said p+ impurity doped regions; and applying an electrically conductive material to the exposed major surface of said nonconductive layer in a predetermined pattern, said electrically conductive material making electrical contact to the p+ impurity doped regions.

Claim 12

A method for passivating the back metallization of a solar cell and forming deep impurity doped regions under the back contacts of said solar cell, said method comprising the steps of: providing a p-type wafer of silicon with front and back major essentially parallel surfaces; forming an n + -p junction in said wafer under the front major surface, said junction being disposed between the front and back major surfaces and defining an n+ layer between said junction and the front major surface; maintaining said wafer at a predetermined temperature in the presence of a p-type impurity for a predetermined period of time to produce a p+ layer under said back surface, said p+ layer and said n+ layer defining a p-type layer therebetween; depositing a nonconductive layer upon said back major surface, said nonconductive layer having an exposed major surface essentially parallel to said back major surface; screen printing a metal paste in a predetermined pattern onto the exposed major surface of said nonconductive layer, said metal paste comprising fine metal particles suspended in a vehicle; heating said wafer and metal paste to a predetermined temperature so that said metal paste will oxidize, thus reducing the portion of said nonconductive layer located underneath said metal paste pattern, which remaining metal will continue melting into and alloying with portions of said p+ layer and with portions of said p-type layer to a predetermined depth which is dependent on the temperature and time, and amount of metal paste used; cooling said wafer to form p+ impurity doped regions that extend from at or near said back major surface of said wafer to a predetermined depth into said p-type layer; removing any excess metal and oxide layers formed during the above steps, leaving said nonconductive layer with openings therein extending from the exposed major surface of said nonconductive layer to said p+ impurity doped regions; and applying an electrically conductive material to the exposed major surface of said nonconductive layer in a predetermined pattern, said electrically conductive material making electrical contact to the p+ impurity doped regions.