Reactive silver ink as front contacts for high efficiency silicon heterojunction solar cells

Low-resistance Ohmic contacts formed at low temperatures expand photovoltaic device opportunities to include thermally sensitive layers while reducing thermal budget during fabrication. Silicon heterojunction solar cells cannot be processed over ~200°C because of temperature-induced degradation of surface passivation provided by hydrogenated amorphous silicon. Efficiencies of these cells are limited by high series resistance, which primarily arises from the use of relatively high-resistivity silver paste contacts that are formed at low-temperature. We report the formation of highly conductive contacts by drop-on-demand printing of reactive silver inks at low temperatures between 50 and 110°C, resulting in resistivities approaching that of bulk silver. Reactive silver ink printed as a front grid on a silicon heterojunction solar cell resulted in a cell series resistance of 1.8Ω cm² compared to 1.1Ω cm² for a cell screen printed with low-temperature silver paste. These results show that, before optimization, reactive silver ink contacts perform comparably to pastes that have been custom developed and commercialized for this specific application.