Determining Components of Series Resistance from Measurements on a Finished Cell

Detailed expressions are given for computing the components of series resistance for a cell with a common contact pattern of parallel, equally-spaced gridlines which are perpendicular to two or more busbars. Front busbars and gridlines, contact resistance, emitter sheet, substrate, back metal and back busbars are all considered. No detailed thickness profiles are needed for any feature, only basic lengths and separations along with four-point resistance measurements. Results are given for a two-bus 15 cm square multicrystalline silicon cell having an efficiency of 15.0%. The total series resistance is 1.04 Omega-cm², dominated by the gridline contribution. The addition of a third busbar is calculated to result in an increase in FF of 0.018, corresponding to an increase of 0.36% in absolute efficiency. A method for providing a coarse map of pseudo contact resistance for a finished cell, using only a four-point probe, is also introduced