Non-volatile free silver paste formulation for front-side metallization of silicon solar cells

We present a versatile, cost-effective formulation platform for highly conductive silver pastes used in front-side metallization of silicon (Si) solar cells. Pastes based on the capillary suspension concept include silver particles, glass frit and two immiscible fluids. Capillary forces inferred from the second fluid added only in small fractions induce the formation of a percolating particle network. This provides extended shelf-life and distinct flow properties adjustable in a wide range as demanded by the respective printing process, thus yielding residual-free sintered electrodes. Si-wafers are successfully metallized with such pastes using conventional screen-printing, knotless screen and Pattern Transfer Printing™. Paste spreading is studied via high-speed imaging during screen-printing on glass plates. Morphology of printed lines is analyzed using laser scanning microscopy. Electrical properties of the cells are characterized employing a solar simulator and electroluminescence spectroscopy. Results are compared to those obtained using commercial pastes including the same silver particles and glass frits. Paste performance strongly depends on the selected secondary fluid. Aspect ratios ≈0.4–0.5 can be reached and cell efficiencies ηeff ≈ 21% on Cz- and 18.6% on mc Si-wafers are obtained. Additional investigations are necessary to further reduce paste spreading and line interruptions thus improving cell performance.