Impact of metal contact misalignment in silicon ink selective emitter solar cells

A selective emitter is a front-contact solar cell configuration in which surface regions under the front contacts are heavily doped to improve ohmic contact, while remaining emitter surface regions are lightly doped to minimize charge carrier recombination and improve blue spectrum response. Since the highly doped regions are relatively narrow, front contact misalignment will tend to have a detrimental impact on cell performance. In this report we quantify the impact of misalignment for solar cells manufactured with Innovalight Cougar™ Platform and Innovalight Silicon Ink. The Innovalight Cougar™ Platform is a portfolio of simple to implement technologies that, when combined with Innovalight Silicon Ink, enables the manufacture of a selective emitter (SE) solar cell with a non-masking single-step diffusion. Innovalight Silicon Ink, used to create the heavily doped regions, is a highly engineered silicon nanoparticle colloidal dispersion, implemented for both high volume inkjet and screen deposition, and further optimized to be produced and delivered in commercial volumes. Test cells were fabricated with a set of varying offsets between the highly doped regions and front silver features, thus controlling the amount of translation misalignment. We characterized the alignment accuracy by an automated vision system and report center-to-center offset values of less than ±10 μm for cells with designed offset of zero (see also). We demonstrate the cell performance remains unchanged, as long as the silver print does not extend past the highly doped regions (as defined by the deposited Innovalight Silicon Ink). For increasing misalignment offset, the major impact is an increase in series resistance resulting in a 26 % reduction in fill factor. Additionally, the open circuit voltage and short circuit current of the Cougar cells are reduced by 1-2 % due to increased recombination in the emitter. Taking tolerances of an industrial-scale production process into account, the processing window to ensure optimal cell performance without degradation due to misalignment of metal and SE pattern is specified.