Methods for wet chemistry polishing for improved low viscosity printing in solar cell fabrication

A method of fabricating a solar cell, the solar cell having a front side which faces the sun during normal operation and a back side opposite the front side, the method comprising:

• forming a polished surface on a silicon substrate using an etchant, wherein the polished surface has at most 500 nanometer peak-to-valley roughness and is formed on the back side of the solar cell;
• depositing first and second dopant material, each dopant material having a viscosity in the range of 1-25 centipoise (cP), in an interdigitated pattern on the polished surface, the first and second dopant materials comprising a first and second dopant source, respectively, wherein the polished surface allows the first and second dopant materials to form an interdigitated pattern comprising features of uniform thickness and width;
• heating the silicon substrate and the first and second dopant materials to a temperature sufficient to cause the first and second dopant sources to diffuse into the silicon substrate forming a first and second doped regions within the silicon substrate;
• depositing a first dielectric layer over the first and second doped regions;
• forming a plurality of contact openings within the first dielectric layer;
• forming a first metal layer established through the contact openings over the first and second doped regions, wherein the first metal layer comprises electrically connected grids to the first and second doped regions on the back side;
• and
• forming a second metal layer on the first metal layer, wherein the first metal layer electrically couples the second metal layer to the first and second doped regions.

A method of fabricating a solar cell, the solar cell having a front side which faces the sun during normal operation and a back side opposite the front side, the method comprising:

• forming a polished surface on a silicon substrate using an isotropic etchant, wherein the polished surface has at most 500 nanometer peak-to-valley roughness and is formed on the back side of the solar cell;
• forming first and second doped regions on the back side of the solar cell;
• depositing a first dielectric layer over the first and second doped regions;
• forming a plurality of contact openings within the first dielectric layer;
• depositing a first metal paste to at least fill at least one contact opening established through the dielectric layer formed over the first and second doped regions, wherein the topography of the first and second doped regions is conformal with the polished surface of the silicon substrate;
• depositing a second metal paste to connect more than one contact opening filled with the first metal paste to form interdigitated patterns over the dielectric layer on the back side, wherein the second metal paste is deposited by industrial printing methods over the polished surface such that the topography of the second metal paste is conformal with the polished surface of the silicon substrate;
• curing the first and second metal paste to form a first metal layer comprising electrically connected grids to the first and second doped regions on the back side;
• and
• forming a second metal layer on the first metal layer, wherein the first metal layer electrically couples the second metal layer to the first and second doped regions.