Passivation of screen-printed aluminium-alloyed emitters for back junction n-type silicon solar cells

We present a detailed study on effectively surface-passivated aluminium-doped p+ emitters to further enhance the efficiency of our n-type silicon solar cells featuring a full-area screen-printed Al-alloyed rear emitter. We investigated two different passivation layers both well suited for highly doped p+ silicon: plasma-enhancedchemical- vapour-deposited amorphous silicon (a-Si) and atomic-layer-deposited aluminium oxide (Al2O3). We show that for an effective emitter passivation (i) a careful preparation of the emitter surface and (ii) low emitter thicknesses are essential. Combining these two aspects, we have achieved extraordinary high implied open-circuit voltages of 673 mV for a-Si- and 679 mV for Al2O3-passivated Al-alloyed emitters, corresponding to emitter saturation current densities of 128 fA/cm2 and 89 fA/cm2, respectively.