Application of plasma enhanced chemical vapor deposition silicon nitride as a double layer antireflection coating and passivation layer for polysilicon solar cells

Abstract

Reflection losses in passivated emitter solar cell polycrystalline silicon solar cells have been reduced by the application of a double layer antireflection coating of plasma enhanced chemical vapor deposition silicon nitride (PECVD SixNyHz). The layer was deposited in a single wafer parallel plate reactor powered by a 13.56 MHz rf power supply using SiH4 and NH3 as the reactive gases. The layers deposited had refractive indexes of 2.50 and 1.95 at HeNe wavelength and thicknesses of 42.5 and 64.5 nanometers (nm), respectively. The overall reflectance measured in the wavelength range between 350 and 1150 nm was 8.5%. The extinction coefficient of the high refractive index film showed a significant increase in absorption for short wavelengths. However, the improvement in current collection was higher than expected from the overall reflectance and absorption of the film. Short circuit current was increased by 49% and open circuit voltage increased by 3.3% when compared with uncoated cells. These results imply a passivation effect which increases the open circuit voltage beyond the value expected solely from the current collection addition.