Sputtering for the Formation of Si-Based Passivating Contacts

We investigate the electrical properties of electron-selective passivating contacts based on thin tunnel oxide capped by a phosphorus-doped poly-Si layer. The poly-Si formation relies on the sputtering of the amorphous-Si layer subsequently annealed. We study the impact of the doping method, the phosphorus content of the Si target, sputtering parameters as well as annealing temperature on surface passivation and carrier extraction. The possibility to deposit in the same sputtering tool both the tunnel oxide and the poly-Si layer is also investigated. It is found that similar levels of implied V _OC and contact resistivity are attained when the tunnel oxide is grown chemically or deposited by sputtering. In-situ doping of the silicon layer with doped Si targets leads to the same level of passivation and carrier extraction than when the doping is performed in a second step, ex-situ, by POCl ₃ or plasma-assisted process, with values of implied V _OC above 730 mV and contact resistivity down to 2 mΩ.cm ² . The implementation of such sputtered poly-Si at the rear side of n-passivated emitter rear totally diffused (n-PERT) solar cells enabled to reach certified cell efficiency of 22.8% with V _OC of 697 mV and fill factor (FF) of 80.5%.