Self-doping contacts to silicon using silver coated with a dopant source [for solar cells]

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 SIMS analyses all indicate that the Ag-Si eutectic temperature (835/spl deg/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 m/spl Omega/-cm/sup 2/ contact resistance directly to 7 /spl Omega/-cm n-type dendritic web silicon. For contacting lightly-doped n/sup +/ layers (<100 /spl Omega///spl square/) through SiN/sub x/, a fritted version is used. The resultant contact metal is highly conductive (3 /spl mu//spl Omega/-cm) and solderable. No carrier lifetime degradation associated with the alloying process has been observed in dendritic web silicon solar cells.