Front SiON/TCO Stacks Development for Double-Side Poly-Si/SiOX Passivated Contacts Solar Cells

This article reports on the use of a front-side SiON/transparent conductive oxide (TCO) bilayer in double-side poly-Si/SiO_X-based passivated contacts solar cells. This approach presents the advantage of a low indium consumption either by reducing the indium-based TCO thickness or by enhancing its substitution with a zinc-based TCO, such as aluminum-doped zinc oxide (AZO). Thickness optimizations with optical simulations have been performed. An electrical study with a TCO thickness reduced to 20 nm on textured surfaces has shown excellent responses for SiON/TCO stacks, especially regarding the contact resistivity. Finally, the developed SiON/TCO bilayers were integrated in complete solar cells. Interestingly, the substitution of the standard 70-nm-thick ITO layer by a 20-nm-thick ITO film covered by SiON led to an efficiency gain of +0.2% abs. Regarding AZO, the replacement of the standard 70-nm-thick AZO layer by a 20-nm-thick AZO film covered by SiON resulted in a J_SC gain of +0.7 mA/cm². These gains in performances could be raised with further posttreatments. However, the current results already confirm the possibility to optimize thin-poly-Si-based passivated contacts solar cells toward In-free fabrication processes.