High Throughput Low Energy Industrial Emitter Diffusion and Oxidation

In this work, we investigate an approach of shortened low pressure (LP) POCl3 diffusion and a high throughput thermal oxidation with stacked wafers to form the emitter for passivated emitter and rear cells (PERC). As the high temperature processes such as LP-POCl3 diffusion and thermal oxidation account for a significant share of the manufacturing costs of PERC solar cells, our high throughput approach is very promising in terms of reducing both, production costs and energy consumption. Compared to state-of-the-art POCl3 diffusion and low temperature oxidation, a 40% reduction of the specific costs and a 50% reduction of the energy consumption of the high temperature processes is feasible. We examine this approach by using four different adapted LP-POCl3 diffusion processes using only the deposition phase (omitting further drive-in and in-situ oxidation) in combination with a ""stack oxidation"" process. Detailed characterization of the properties of the emitter and oxide layers after diffusion and after oxidation confirm a high quality emitter formation resulting in emitter dark saturation current density j0e ≈ 32 fA/cm2 at Rsh ≈ 183 Ω/sq. Although the wafers are oxidized in a stack of horizontally oriented wafers touching each neighboring wafer, a very homogeneous oxide grows resulting in high passivation quality. Further, we find that this adapted emitter diffusion process allows for effective laser doping, which is promising for selective emitter formation.