Back contacted photovoltaic cell with an improved shunt resistance
The invention relates to a photovoltaic cell, comprising a plate shaped substrate of a semiconductor material with a solar face and a connection face, a first volume of the substrate adjacent to the solar face is doped with a first polarity, the second volume is doped with a second polarity and the volumes are separated by a pn-junction, a number of apertures in the substrate extending between both faces and in which a plug has been positioned of which a part is conducting, contact tracks at the solar face of the substrate connected with the first volume and the conducting part of the plug, first contacts at the connection face of the substrate connected with the conducting part of the plug and second contacts located at the connection face of the substrate connected with the second volume, wherein the specific electrical conductivity of the plug decreases from its centre to the contact face with the substrate.
1. A photovoltaic cell, comprising:
a plate shaped substrate of a semiconductor material with a solar face and a connection face, wherein a first volume of the substrate adjacent to the solar face is doped with a first polarity, the remaining second volume of the substrate is doped with a second polarity opposite the first polarity and in which the first and the second volumes are separated by a pn-junction extending parallel to the main plane of the substrate;
a number of through apertures in the substrate extending between both faces of the substrate and in each of which a single piece plug has been positioned of which at least a part is electrically conducting, which part is adapted to provide an electrical conducting connection between the solar face and the connection face;
contact tracks located at the solar face of the substrate and being electrically connected with the first volume of the substrate and with the electrically conducting part of the plug;
first contacts located at the connection face of the substrate and being electrically connected with the electrically conducting part of the plug; and
second contacts located at the connection face of the substrate and being electrically connected with the second volume of the substrate, wherein the specific electrical conductivity of the plug decreases from its centre to its circumferential boundaries.
2. The photovoltaic cell as claimed in claim 1 , wherein the plugs each comprise an electrically insulating jacket surrounding at least a section of the electrically conducting part of the plugs.
3. The photovoltaic cell as claimed in claim 2 , wherein the electrically insulating jackets extend over the full thickness of the substrate.
4. The photovoltaic cell as claimed in claim 2 , wherein the electrically insulating jackets extend over a section of the thickness of the substrate.
5. The photovoltaic cell as claimed in claim 2 , wherein the specific resistance of the electrically insulating jacket at its contact face with the substrate is greater than the specific resistance of the material of the substrate at the contact face with the electrically insulating jacket.
6. The photovoltaic cell as claimed in claim 5 , wherein the plugs are fused with or soldered to the contact tracks on the solar face of the substrate.
7. The photovoltaic cell as claimed in claim 1 , wherein the plugs are cylindrical.
8. The photovoltaic cell as claimed in claim 1 , wherein the plugs are formed by heating and subsequent cooling of a paste.
9. The photovoltaic cell as claimed in claim 1 , wherein the contact tracks located at the solar face of the substrate, the first contacts and the plugs in the through apertures contain at least one same metal.
10. The photovoltaic cell as claimed in claim 1 , wherein the plugs comprises a mixture of electrically conducting particles and electrically insulating particles in an organic medium.
11. The photovoltaic cell as claimed in claim 1 , wherein the boundary between the substrate and the apertures is covered by a passivation layer.
12. The photovoltaic cell as claimed in claim 11 , wherein the passivation layer extends also over the solar face of the substrate and that the contact tracks extend through the passivation layer in contact with the first volume.