Ultrathin SiOx layers and c-Si/SiOx interfaces find application in tunnel-oxide passivated
contacts (TOPcon) for high-efficiency silicon solar cells. Here, we investigate their detailed
microscopic properties, with specific attention for the case of c-Si(100) substrates, capped either
by p-type or n-type poly-silicon layers [c-Si/SiOx/poly-Si (p+) or c-Si/SiOx/poly-Si (n+)]. Our
focus is on the effects of the substrate preparation conditions (either by a dry-plasma or wet
SiOx process) and the high-temperature annealing step (as required for the poly-Si
crystallization) on the SiOx stoichiometry and its microscopic structure. Through advanced
photoemission techniques, we find a clear decreased valence band offset between the c-Si and
SiOx (from 4.5 eV to 4.15 eV) when comparing the dry SiOx with the wet SiOx process,
independent of the SiOx film thickness, but correlating with the relative fraction of substochiometric Si states. We lastly examine the magnitude of band-bending of the contact
structure through controlled in-situ exposure to light of the surfaces and subsequent tracking of core and valence band levels via a surface photovoltage and a junction photo-voltage (JPV)
effect. By analyzing this JPV effect qualitatively, we find it to be proportional to the expected
quasi fermi level splitting within the c-Si wafer.
