Study of screen printed metallization for polysilicon based passivating contacts

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 J_o, 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 V_oc 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 V_oc 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 V_oc-based) rendering values for the prefactor of the recombination current J_o,c at the contact areas of about 400 and 350 fA/cm² for 200 nm thick n-polySi and p-polySi, respectively.