TiN x and TiO x /TiN x Barrier Layers for Al‐Based Metallization of Passivating Contacts in Si Solar Cells

A solution is presented for Ag‐free contacting of passivating contacts for crystalline Si‐based solar cells. In particular, a Ti‐based diffusion barrier layer is introduced between the polycrystalline‐Si of the passivating contact and standard screen‐printed Al‐paste, in order to prevent Al/Si alloying during contact sintering. This solution enables contact formation with industrial standard Al‐pastes while maintaining high surface passivation quality of the underlying passivating contact. Metallization‐induced implied open circuit voltage losses remain below 10 mV, with values > 720 mV before metallization. Contact resistivity values are below 3 Ωcm on average at substrate peak firing temperatures of 700 °C. This approach provides an alternative to Ag‐based contact electrodes, while still maintaining high surface passivation quality and enabling low contact resistivity through the use of a conductive barrier layer. Thermal stability of the diffusion barrier and the impact of layer properties on its functionality are investigated. The impact of a TiO x seed layer on diffusion barrier layer orientation is examined. Seed layer dependent properties, such as crystal orientation, are analyzed with X‐ray diffraction. TiN x layer orientation changes with introduction of the TiO x seed layer, enabling a higher peak firing window. Diffusion profiles of Si, Al, and Ti are investigated via secondary‐ion mass spectrometry.