Optimizing Fine Line Dispensed Contact Grids

Previous studies on dispensing as an alternative front side metallization process in crystalline silicon photovoltaics demonstrated, how an adaption of paste rheology allows for a precise adjustment of contact finger geometry in a wide range. In order to demonstrate the benefit of this advantage, the analytical simulation tool Gridmaster was extended to observe the effect of various geometrical parameters on solar cell results and manufacturing costs. In addition, respective geometrical parameters of thick film printed contact fingers were determined using a special in house developed tool based on MATLAB. As a result, contact geometries as achievable by means of ultrafine line dispensing are ideally suited for contacting silicon solar cells. Compared with standard fine line single screen printed finger geometries, an efficiency increase of up to Δη = 0.4%abs. as well as a reduction of manufacturing costs of 1 €ct./Wp on module level can be achieved using dispensing technology. In order to obtain suitable data, simulation results were compared with solar cell results on industrial pre-processed Cz-Si p-type wafer material applying the novel ten nozzle parallel fine line dispensing unit. Therefore, a new dispensing paste was developed combining optimum optical finger aspect ratios of ARo=0.7 with excellent contacting behavior. A successful first test of applicability already led to a maximum cell efficiency of η = 18.7%, demonstrated on an industrial emitter with a sheet resistance of around Rsh = 90 Ω/sq.