Passivation properties of amorphous and microcrystalline silicon layers deposited by VHF-GD for crystalline silicon solar cells

Abstract

A comparative study of crystalline silicon (c-Si) surface passivation techniques is presented. The passivation is essential in increasing the total solar cell efficiency by enhancing the open-circuit voltage ( V oc ). Apart from the thermally grown oxides or nitrides widely used sofar, recent publications report on excellent passivating properties of amorphous silicon (a-Si:H)- and microcrystalline silicon (μc-Si:H) layers, deposited on n-type crystalline silicon [1–3], forming thereby heterojunctions. We present first results of a new structure called ⪡BAP (Both Sides Amorphous Passivated) cell⪢, where the wafer was sandwiched between two intrinsic amorphous silicon layers. These two layers, as well as the μc-Si:H emitter, and the layer forming the BSF (Back Surface Field) were all deposited by the VHF-GD (Very High Frequency Glow-Discharge) process which was developed in our laboratory [4]. BAP cells showed V oc -values as high as 635 mV, proving thus the excellent passivating properties of a-Si:H and the validity of this cell concept which makes a fully in-line processing possible (wafer in-cell out).