MonoPoly™ cells: Large-area crystalline silicon solar cells with fire-through screen printed contact to doped polysilicon surfaces

Abstract

Successful integration of carrier selective contacts (so-called passivated contacts) in p-type and n-type front-and-back contact (FAB) silicon solar cells could lift cell efficiencies to above 24% in mass production. In this work, we introduce one of SERIS’ monoPoly FAB cell structures, which features the monofacial (single-sided) application of a polysilicon (poly-Si) layer. Using industrial tools, doped poly-Si on an ultrathin interface oxide is shown to provide extremely low recombination current density of 4 fA/cm2 and implied open-circuit voltage of about 745 mV that are able to withstand the high-temperature firing process of screen-printed metal contacts. The interface oxide and the doping concentration of the poly-Si film are of great importance for the surface passivation quality and the transport of majority carriers, especially for fire-through screen-printed contacts as used in this work. Our initial pilot-line results show a very promising cell efficiency of 21.4% on large-area (244.3 cm2) n-type monocrystalline wafers with screen-printed and fire-through metal contacts on both sides. A roadmap for nFAB monoPoly cells towards 24% efficiency is presented on the basis of an optimisation of the device architecture and various processing steps.