Transfer-Length Method Measurements Under Variable Illumination to Investigate Hole-Selective Passivating Contacts on c-Si(p) and c-Si(n) Wafers

In this article, transfer length method (TLM) measurements under variable illumination are applied to study p-type carrier selective passivating contacts (CSPCs) employed in the silicon heterojunction (SHJ) technology. In the case of p-type CSPCs deposited on p-type crystalline silicon (c-Si(p)) wafers, we demonstrate that illumination has a strong impact on the contact resistivity (rho(c)) value, as demonstrated in our previous contribution in the case of n-type CSPCs on c-Si(n). Noticeably, it was again found that rho c increases and that the c-Si sheet resistance (R-sh) decreases with the illumination. In addition, we demonstrate that rho(c) is impacted differently by illumination depending on the doping of the p-type thin hydrogenated silicon layer. Then, we investigate and discuss the applicability of TLM measurements under illumination to measure p-type CSPCs deposited on their inverse type c-Si(n) wafers. First, performing TLM measurement in dark conditions of such samples allow one to measure R-sh values with orders of magnitude corresponding to the c-Si(n) inversion layer one. Second, we demonstrate that under illumination, the lateral transport inside the c-Si(n) bulk is supported by the electrons thanks to two experimental evidences, i.e., that the R-sh behavior as a function of injection behaves as the one of electrons and that an electron transport inside the c-Si(n) wafer in the presence of two p-type CSPCs TLM pads can only be mediated thanks to photogeneration under one pad and recombination under the other. These results provide additional understandings of the TLM measurement under illumination as well as strong insights for the investigation of carriers' transport and electrical losses in CSPCs solar cells.