Laser-induced modification of doped poly-Si surface for Si solar cells with structured passivated contacts

Passivated contacts that use polysilicon on oxide (POLO) show outstanding electrical surface passivation of silicon. However, the parasitic absorption of photons within highly doped poly-Si layer confines its implementation to the rear side silicon solar cells or locally under the front metal contacts. Here, we demonstrate that by irradiating the poly-Si with UV ps-laser pulses, it becomes selectively etch resistant in a KOH solution, due to a laser-induced amorphization of the surface of the poly-Si layer. This poses a low-effort method to structure poly-Si layers with a resolution of the spot size of 25 μm and thus facilitates the implementation as local (front) contacts. We explore the impact of the laser fluence, the gas ambient and the surface morphology (planar and textured) on the surface passivation quality of the so obtained poly-Si layers. The laser-modified and structured poly-Si sample reaches implied open-circuit voltage values of iVoc = 722 mV (planar) and thus the same passivation quality as the non-lasered reference, and iVoc = 680 mV for textured surfaces. A hydrogenation step improves the iVoc of the textured surfaces to 726 mV, which corresponds to a recombination current density of 5 fA/cm2.