We report effect of nanostructured silicon rich silicon nitride (SRSN) thin films of different thickness as a top layer on Si-solar cell on various characteristics including efficiency of the cells. Thin films of various thickness were grown on Si substrate by plasma enhanced chemical vapor deposition. Sharp reflection minima in the solar spectral range is obtained after coating. Further, current voltage characteristics were studied for solar cells with SRSN layers of different thickness. Highest efficiency value of similar to 9.9% were obtained for cell with 180 nm SRSN coating on top, showing a significant increase in efficiency as compared to solar cell without SRSN coatings. This is understood by critically analyzing all parameters for this cell in the framework of two diode model. Lower series resistance, high shunt resistance and maximum fill factor of this film leads to highest efficiency.