Influence of Plasma-Enhanced Chemical Vapor Deposition Poly-Si Layer Thickness on the Wrap-Around and the Quantum Efficiency of Bifacial n-TOPCon (Tunnel Oxide Passivated Contact) Solar Cells

In typical industrial processing of tunnel oxide passivated contact (TOPCon) solar cells, poly-Si is deposited on the entire back of the cells. During the deposition process, a wrap-around of poly-Si onto the edges and the front side of the cells is virtually unavoidable if chemical vapor deposition processes are used. Plasma-enhanced chemical vapor deposition (PECVD) is used to investigate very thin poly-Si films and their effect on wrap-around on bifacial TOPCon solar cells fabricated without wrap-around etching. As a result, reduction of the poly-Si thickness down to 30 nm significantly increases the shunt resistance, reduces the reverse bias current, and thus reduces the risk of hot spots as measured by IR imaging and microcharacterization by secondary electron microscopy. Electroplated metallization proves to be a suitable candidate for contacting such thin TOPCon layers, being less sensitive than screen-printed metallization.