Industrial Si Solar Cells With Cu-Based Plated Contacts

Challenges facing copper‐plated metallisation for silicon photovoltaics: Insights from integrated circuit technology development

“…At the time Pluto modules were released into the market, Suntech claimed to be performing advanced levels of environmental testing on its products, and so given these reports it would appear that even if the Cu could penetrate through LIP Ni diffusion barriers in Pluto modules, the electrical performance of modules was not significantly degraded. This conclusion is also supported by a number of other studies which have reported that Ni/Cu plated modules, where the contact regions in the cells had been formed by short pulse laser ablation, have also passed the thermal cycling and damp heat test sequences required by the IEC 61215 standard …”

“…For a Cu‐plated metallisation process to be commercially viable, plated cells will need to achieve similar or superior efficiencies to comparative screen‐printed cells. Many reports have highlighted the potential of Cu‐plated cells to out‐perform screen‐printed cells, due to their narrower fingers resulting in reduced shading and the ability of Ni to form ohmic contact to Si surfaces with P concentrations as low as 4 × 10 19 cm ‐3 and potentially even lower . However, these attributes only provide an advantage if other sources of loss are not introduced during the metallisation process.…”

“…Metallisation of solar cells introduces contact recombination if the metal is in direct contact with the Si of the cell. The doping density of the Si at the surface directly affects the recombination current density under the metal, so whilst it may seem beneficial for Ni/Cu plated contacts to be able to form ohmic contacts to Si surfaces with P concentrations as low as 4 × 10 19 cm ‐3 , the reduced emitter recombination current density, that results from adoption of more lightly doped emitters, may be achieved at the cost of a larger contact recombination current density due to the higher concentration of minority carriers at the metal‐Si surface …”

“…This non‐uniform growth can increase non‐ideal ( n = 2) recombination and present an effective metal‐Si area that is larger than the projected area of the contact on the surface. To some extent, this problem can be addressed by engineering a deeper junction; however, the longer diffusion times required to form deeper junctions may not always be justified in a manufacturing environment.…”

“…Potential efficiency and yield gains for Cu‐plated cells over screen‐printed cells have also been frequently suggested. These gains include reduced front surface shading and the electrical contacting of more lightly doped emitters . Self‐alignment of Cu‐plated contacts may also be advantageous for more complex cell structures .…”