Industrial High Throughput Emitter Formation and Thermal Oxidation for Silicon Solar Cells by the High Temperature Stack Oxidation Approach
Herein, the high temperature stack oxidation (HiTSOx) approach for the fabrication of passivated emitter and rear cells (PERCs) is investigated. This approach features a combination of phosphorus oxychloride (POCl3) diffusion shortened to the phosphosilicate glass (PSG) deposition phase as well as high temperature thermal oxidation using stacked wafers. During the latter thermal oxidation, the incorporated phosphorus is redistributed and diffuses deeper into the silicon wafer. The simultaneously growing thermal dioxide serves as a passivation layer. Due to the use of stacked wafers, the throughput of the HiTSOx approach is three times higher in comparison to state-of-the-art oxidation at moderate temperature. Applying a busbarless metallization layout, a median energy conversion efficiency of i = 22.2% is achieved for the HiTSOx approach, being similar to the performance of the reference group with state-of-the-art PERC processing also with i = 22.2%. Despite stacking of the wafers during the thermal oxidation, an excellent homogeneity of the oxide layer thickness of ±1 nm over the wafer surface is found, whereas the passivation quality features dark saturation current densities j0e as low as j0e = (30 ± 3) fA cm−2 at emitter sheet resistances Rsh = (199 ± 6) O sq−1.