In the crystalline silicon soalr cell fabrication process P-types wafer (boron doped) is taken and n+ (Phosphorus) is diffusied.
What is the criteria to select the back contact material?
Can i use Silver as a back contact or i have to aluminum only.
If I have to use aluminium only what is the reasion.
The criteria for selecting a crystalline silicon solar cell back contact material should include:
1. High electrical conductivity
2. Low contact resistance
3. Chemical compatibility with the silicon solar cell
4. Thermal stability
5. Low cost
6. Easy processing
7. Thermal and electrical insulation
Thirty years of technology may have changed things; however, sintering an aluminum back contact after diffusion of the n+ front contact always gave us (COMSAT Labs) better Voc and Isc. We attributed that to gettering of the bulk Si (and we measured the improvement of lifetime in the p layer). If the diffusion length is already optimized after fabrication, a backside p+ layer (with grown oxide reflective coating) improves beginning-of-life performance by reducing the back-surface recombination velocity and long-wave optical absorption of the Al ohmic contact. Instead of gridded back contacts, dot contacts, with a full silver backing, reduces the area of the ohmic contact recombination velocity and its long-wave optical absorption. This technique allows thin cells to have higher Voc and fill factor without losing Isc.
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