NOX-free edge isolation and polishing
The Alkaline Edge Isolation Inline System combines several process steps in a modular system. On the one hand the emitter layer on the rearside of the wafer generated during the diffusion process is unilaterally isolated from the front side of the wafer in order to prevent malfunction of the solar cell. On the other hand the phosphorous-silicate glass (PSG) is removed from the wafer surface.
With the Alkaline Edge Isolation Inline System, SCHMID has the world’s only system for edge isolation in its portfolio which can be operated without any nitric acid (HNO3). Alkaline potassium hydroxide solution (KOH) is used instead of the expensive acid. The obvious advantages: No nitrogen oxide (NOX) is generated, which requires a complex exhaust and a subsequent costly disposal. This allows to easily meet increasingly stringent environmental requirements. In addition, processing at about 90 °C ensures a high etching rate and thus a small footprint of the system.
During the edge isolation the emitter is protected by the water mask developed and patented by SCHMID. Special transport rollers ensure that the chemistry comes into contact exclusively with the rearside, thus reducing the chemistry consumption. In addition the process can be used for polishing the rearside of high efficiency cells such as PERC. Further to significant cost savings, the process also allows additional performance improvements.