Enhanced current collection in back-contacted back-junction Si solar cells by overcompensating a boron emitter with a phosphorus base-type doping

Electrical shadings losses, resulting from a reduced minority charge carrier collection probability in regions without a collecting p-n junction, of industrially fabricated back-contacted back-junction silicon solar cells, are one of the main loss mechanisms. In order to minimize these losses, a local overcompensation of a boron emitter doping with a phosphorus base-type doping can be applied to reduce the area without a collecting p-n junction and to increase the emitter coverage on the rear side considerably. The focus of the present investigation is to analyze the influence of the aforementioned solar cell design on the locally measured external quantum efficiency (EQE) and on the short-circuit current. It has been found that for solar cells with a reduced base-type doping area and an increased emitter coverage, electrical shading losses could be minimized significantly, resulting in very high short-circuit currents J(sc) of 39.8 mA/cm(2) for a 1 Omega cm and 40.9 mA/cm(2) for a 10 Omega cm base material. This corresponds to a gain in J(sc) of 2.4 and 1.0 mA/cm(2), respectively, compared to reference solar cells with a reduced collecting p-n junction area.