The Effect of ZnO Sputtering Deposition Parameters on the Performances of Back Reflector Enhanced Amorphous Silicon Solar Cells

Abstract

ABSTRACTLow resistivity (5×10−4Ω cm) and high transmittance (T > 82 %) ZnO films have been obtained by RF magnetron sputtering deposition of ZnO/Al2O3 (2.5 % wt.) target. The doped oxide films have been investigated by optical and electrical measurements and by scanning electron microscopy. The optimized recipes have been applied to the realisation of amorphous p-i-n solar cells back reflector in the structure: TCO/pin/ZnO/Ag.The application of ZnO/Ag leads to an increase of the Jsc current of about 13% but a poorer fill factor steadily affects the characteristics of the devices. We demonstrate that a thicker n+ layer of about three times the standard one is effective in driving the FF toward the normal values.The cells' behaviour has been ascribed to a thinning of the n+ layer resulting from a sputtering action of energetic oxygen atoms during the ZnO deposition process. This effect has been evidenced by measuring the absorbance of SnO2/a-Si (20 nm) /ZnO in comparison with SnO2/a-Si (20 nm) structure.