Computational Modeling of Polycrystalline Silicon on Oxide Passivating Contact for Silicon Solar Cells

Polycrystalline silicon on oxide (POLO) junction passivating contacts have recently been demonstrated as carrier selective contacts for high-efficiency silicon solar cells. The carrier transport through these contacts has been attributed to two competing mechanisms: 1) carrier tunneling through ultrathin oxide and 2) transport through weak spots (pinholes) - the nanoscale regions where oxide thickness has been completely or partially compromised during the processing. In this paper, we use two dimensional device simulations to compare the relative effects of these mechanisms on solar cell characteristics with ntype POLO contact. We show that variation in pinhole areal density (D _ph ) or the tunnel oxide thickness (tox) both result in qualitatively similar trends in the cell characteristics under dark and light. For a given tox, an exponential variation in Dph results in trends that are similar to those for a linear variation in tox. The effect of pinholes on contact resistance (ρc) and saturation current density (Jo) is most significant for relatively thicker oxides (≥ 2 nm). For tox ≤ 1 nm, ρc and Jo become essentially insensitive to pinholes for Dph <; 10 ¹⁰ cm ^-2 . The modeling results are compared with a set of published experimental data to predict the possible roles of various mechanisms.