Abstract (EN)

In the context of high-efficiency solar cells based on crystalline silicon (c-Si), the integration of passivating contacts between the metal electrodes and the c-Si substrate has been identified as the next step to further improve the photovoltaic conversion efficiency. Passivating contacts consisting of a highly-doped poly-crystalline silicon (poly-Si) layer on top of a thin layer of silicon oxide (SiOx) offer the most promising approach to bridge the gap between device efficiencies in R&D and those in production. However, so far, their development has mainly proceeded through “trial and error” resulting in a limited understanding of their underlying working principle. More specifically, the surface passivation provided by the poly-Si contact is a combination of different mechanisms, among which the limiting one is still unclear due to: i) the interplay between these different mechanisms and ii) the challenge of characterizing thin-film stacks with features down to the nanometric range. Moreover, p-type poly-Si contacts, which are of prime interest since they could provide an alternative to the conventional contact at the rear side of mainstream p-type c-Si solar cells, have so far demonstrated lower passivation properties than their n-type counterparts, the fundamental reason for this difference remaining unclear.

Within the SLICE project, a dedicated methodology based on lifetime spectroscopy (adapted to the c-Si surface for the purpose of this work) will be applied to identify electrically active defects limiting the lifetime of charge carriers at the interface between the poly-Si contact and the c-Si.  The investigation of different thin-film passivating stacks of iterative complexity will enable to relate their properties to their fabrication process. The insights gained from this unprecedented characterization of defects limiting the interface will provide guidelines for further optimization of poly-Si contacts toward higher passivation performances.