Process development and integration of double-side Poly-Si passivated solar cells with printed contacts via LPCVD and ex-situ tube diffusion

Tunnel oxide passivated contact (TOPCon) solar cells incorporate doped polycrystalline silicon (poly-Si) thin films to promote charge carrier selectivity and supress recombination, and thus enable very high efficiency. So far, most of TOPCon cells only adopt poly-Si at rear side applications due to its absorptive natures. In this work, we have developed suitable n+ and p+ poly-Si layers via low pressure chemical vapor deposition (LPCVD) and tube diffusion for ex-situ doping. With proper process integration, the fabricated double-side poly-Si solar cells consist of ~20 nm n+ poly-Si grown at front textured surface and ~150 nm p+ poly-Si at rear planar surface. An excellent implied open-circuit voltage (iVoc) of 725 mV with a total J0 value of 16.3 fA/cm2 were obtained on cell precursors capped and hydrogenated by SiNx. We also demonstrated solar cell fabrication and metallisation via industry-viable screen printing, which eliminates the use of transparent conductive oxide (TCO). The phosphosilicate glass (PSG) is found as the key point that determines the firing stabilities. The champion cell implemented with fire-through contacts shows a proof-of-concept efficiency of 19.6% over an area of 196 cm2, which is comparable with the reference cell metallised with the help of a tin-doped indium oxide (ITO) layer.