SELF-DOPING CONTACTS TO SILICON USING SILVER COATED WITH A DOPANT SOURCE

Abstract

A contact system for silicon solar cells is described in which silver is coated with a layer of dopant and alloyed with silicon, thereby simultaneously doping the silicon substrate and forming a low-resistance ohmic contact to it. The concept has been demonstrated using evaporated silver with commercially available phosphorus and boron liquid dopants. Silicon surface topography, along with I-V and SlMS analyses all indicate that the Ag-Si eutectic temperature (835°C) must be exceeded and the dopant coating must be present for the contact to be self-doping. The concept has also been implemented in the form of screen-printable silver pastes with phosphorus. A fritless version of the paste exhibited only 3 mR-cm2 contact resistance directly to 7 0-cm n-type dendritic web silicon. For contacting lightly-doped n+ layers (< 100 WO) through SiNx, a fritted version is used. The resultant contact metal is highly conductive (3 pCl-cm) and solderable. No carrier lifetime degradation associated with the alloying process has been observed in dendritic web silicon solar cells.