Growth of graded SixNy ARC films to enhance the efficiency of multi-crystalline silicon solar cells and applicable in high volume production

Abstract

Optimized silicon nitride (SiN) film, which acts as an Anti-Reflection Coating (ARC), surface and bulk passivating layer is the key to enhance the efficiency in silicon solar cells particularly in multicrystalline silicon solar cells. In this work, SiN films with graded and non-graded profiles with different refractive indices have been prepared. The efficiency of a multi-crystalline silicon solar cell has been measured and followed by a module making process to evaluate the cell-to-module conversion power loss (CTMPL). It has been found that an optimized graded SiN film can reduce the surface reflection in ultraviolet (UV) and visible wavelength region significantly and hence enhances the efficiency compared to single step (non-graded) recipe. To develop more insight of the experimental work, simulation was carried out using PC1D solar cell simulator and it has been observed that refractive index (n) of 2.04 is the optimum value of refractive index in single step recipe as it enhances efficiency on cell level measurement among all different single step SiN recipes. Whereas, refractive index of 2.14 is the optimum value of refractive index in graded step recipe as it produces much higher efficiency on cell level measurement among all SiN recipes and even better than single step recipe. In this research work, it has been found that graded step refractive index recipe has reduced the reflectance of SiN films, enhanced spectral response and efficiency of the solar cells and higher refractive index of SiN film corresponds to reduced CTMPL values of the modules.