Study of screen printed metallization for polysilicon based passivating contacts

Abstract

We investigate contacting of n- and p-type polysilicon (polySi) passivating contact layers with industrial screen-printed metal pastes, examining both fire through (FT) and non-fire through (NFT) pastes. The n- and p-type polySi layers, deposited by low pressure chemical vapour deposition and doped by POCl3 diffusion, phosphorus implant, or BBr3 diffusion, result in excellent Jo, even for 50 nm thickness (<2 fA/cm2 for n-polySi, <10 fA/cm2 for p-polySi). The contact recombination is investigated by photoluminescence, and by cell test structures to determine Voc as a function of metallization fraction. The contact resistance is investigated by transfer length method (TLM). The contacts are also extensively studied by high resolution electron microscopy. All-polySi solar cells (i.e., cells with front and back carrier selective layers consisting of polySi) are prepared. Excellent implied Voc values of nearly 730 mV and 710 mV are obtained on the un-metallized polished and textured cells, respectively. The contact recombination after applying screen printed metallization can be analyzed well with both methods (PL and Voc-based) rendering values for the prefactor of the recombination current Jo,c at the contact areas of about 400 and 350 fA/cm2 for 200 nm thick n-polySi and p-polySi, respectively.