Current Collection at Grain Boundaries of mc Silicon Solar Cells: Applied Measurements and Processes, Preparations and Experiments

Grain boundaries exert significant influence on the electrical and optical properties of mc-silicon solar cells. Grain boundaries tend to have a high concentration of lattice defects and impurities which due to high recombination for minority carriers. The usual way of countering these effects is to passivate the grain boundaries with hydrogen atoms.In this work another method has been investigated: The front metal grid of the solar cell has been designed such that it mainly follows the grain boundaries. Theoretically, this entails some beneficial effects:- The shading due to the metal lines is over areas of short lifetime, thereby exposing more long lifetime area to sun light. This should increase the short circuit current.- The metal lines can be thicker, which reduces the series resistance.- Grain boundaries are regions of stronger n-doping. Placing the metal lines there reduces the contact resistance between the metal and the semiconductor.- The electrons in the n-doped emitter drifting to the metal lines do not have to cross the potential barriers at the grain boundaries. This, too, reduces the series resistance.