Selective Emitter Technology

The basic structure of silicon solar cells is based on two positive and negative doped areas. The charge carriers generated by the photo effect are separated by this p-n junction and conducted externally via metal contacts on both sides. The emitter doping is always a compromise in standard solar cells with homogenous emitters. A high n-doping is required in the emitter layer to minimize the resistivity between semiconductor and metal contacts. However, recombination losses increase with rising phosphorous concentration which has an adverse impact on power generation.

Thanks to selective emitter technology from centrotherm photovoltaics, the phosphorous concentration in the emitter can be controlled, so that only the area of the front side metal grid has a high phosphorous concentration and therefore a low emitter resistivity. The rest of the surface is lower phosphorous doped so that a large part of the cell can be used for electricity generation. This combines an improved solar cell performance with very good ohmic contact.

In comparison to the standard process, an additional production step is required for the manufacture of selective emitter solar cells. After POCl₃ diffusion, some of the phosphor in the phosphosilicate glass is diffused precisely and without any defects into the cell surface.

For this purpose centrotherm offers its own laser process and the related c.LAS laser tool which can increase cell efficiency by up to 0.4%. We have integrated selective emitter technology into our FlexLine Plus turnkey production line and alternatively offer it as an upgrade package for existing lines. This enables both new turnkey customers and customers who have manufactured with our proven standard process technology for many years to benefit from selective emitter technology.