US8512463: Thick-Film Pastes Containing Lead- and Tellurium-oxides, and Their Use in the Manufacture of Semiconductor Devices

This patent documents the invention of an electroconductive thick film paste that allows printing on the front-side of a solar cell with one or more insulating layers. The thick film paste is composed of both an electrically conductive metal, and a bismuth-tellurium-oxide which is diffused into an organic medium. The respective bismuth-tellurium-oxide powder batch materials were loaded into a furnace and heated at 900 C. in an O2 environment to melt the mixture. After this, a layer of phosphorus is diffused onto the front-surface of a silicon substrate, and an insulating and anti-reflection layer is added. Then, an Ag paste for the front electrode is printed on the silicon substrate, while Ag/Al are printed onto the backside. After drying, the materials are fired in an infrared (IR) belt furnace between the approximate temperatures of 750 to 8500 C., for range of time between several seconds to several tens of minutes. This temperature firing profile allows for the burn-off of organic binder materials present in the dried thick film paste, and multiple temperature zones in belt furnaces can support the preferred temperature profile. This process provides a method for manufacturing solar cells with good efficiency.

Link to Official Patent: Thick-Film Pastes... and Their Use in the Manufacture of Semiconductor Devices

Keyword: Thick Film