Methods and devices for ultra smooth substrate for use in thin film solar cell manufacturing

1. A substrate smoothening method comprising:

providing a metal substrate with a front surface having substantially flat surface portions and protruded surface portions;

rough finishing the metal substrate to have an Ra in the range of about 0.2 to about 0.5 microns;

removing the some of the protruded surface portions by etching the some of the protruded surface portions to form exposed substrate sections of the metal substrate, wherein the metal substrate has a hardness that prevents smoothening to a desired finish;

flowing a second material into depressed surface portions of the substrate to build up a new top surface having a roughness of about 0.05 microns or smoother;

depositing a contact layer on the second material.

2. The method of claim 1 wherein the contact layer comprises one of tungsten, tantalum, molybdenum, titanium, chromium, ruthenium, iridium and osmium.

3. The method of claim 2 further comprising forming a Group IBIIIAVIA absorber layer over the contact layer.

4. The method of claim 3 , wherein the step of forming the Group IBIIIAVIA absorber layer comprises: forming a precursor layer by electrodepositing the precursor layer comprising copper, indium and gallium; and reacting the precursor layer in presence of at least one of selenium and sulfur at a temperature range of 400 to 600° C.

5. The method of claim 3 further comprising forming a transparent layer over the Group IBIIIAVIA absorber layer, and forming a terminal including busbars and conductive fingers over the transparent layer, wherein the transparent layer includes a buffer layer including one of cadmium sulfide and indium sulfide deposited over the Group IBIIIAVIA layer and a transparent conductive layer including one of zinc oxide, indium tin oxide, and indium zinc oxide deposited over the buffer layer.

6. The method of claim 1 , further comprising forming a protective film on the substrate, wherein the conductive protective film comprises one of ruthenium, osmium and iridium.

7. The method of claim 6 , wherein surfaces of the exposed substrate sections and a top surface of the conductive protective film are substantially coplanar.

8. The method of claim 1 , wherein the step of forming the protective film on the substrate comprises sputter depositing ruthenium.

9. The method of claim 1 , wherein the selective etching is performed during an electropolishing process to planarize the some of the protruded surface portions.

10. The method of claim 1 , wherein the selective etching is performed using an etchant comprising hydrochloric acid.