Contacting Moderately Doped Phosphorous Emitters of Silicon Solar Cells With Dopant Segregation During Nickel Silicidation

Emitter performance is crucial for the efficiency of solar cells. A further increase of efficiency requires reducing recombination losses while keeping parasitic resistances and shadowing at a minimum. In silicon solar cells, recombination can be lowered by decreasing the emitter doping concentration; however, this comes at the cost of increasing contact and sheet resistances. Dopant segregation during nickel silicidation resolves this tradeoff since it allows ohmic contact formation to emitters with almost arbitrary doping profile and concentration. Here, we elaborate on using dopant segregation during silicidation and demonstrate contact formation, as well as a substantial performance improvement of silicon solar cells exhibiting a lowly doped emitter with a peak doping concentration of 6 × 10¹⁸ cm^-3. Furthermore, we show that the small achievable contact resistances in principle allow a strong reduction of the contact area. In turn, this enables lowering the shadowing while, at the same time, decreasing the sheet resistance due to a larger number of front contacts that can be placed close to each other. Using PC1D simulations, we study the solar cell performance as a function of the emitter dopant concentration estimating the achievable efficiency increase when employing dopant segregation.