A triple-layer anti-reflection coating (TL-ARC) with Si nanocrystals (nc-Si)-dielectric nanocomposite thin film structure is proposed for Si solar cells. The TL-ARC has a graded refractive index (RI) profile of high RI, medium RI, and low RI. Such RI profile is achieved with the structure consisting of a Si3N4 layer embedded with high concentration of nc-Si and another Si3N4 layer embedded with low concentration of nc-Si and a SiO2 layer. The design of the TL-ARC is carried out with the calculation of the effective indices of the high-RI and medium-RI layers with the Maxwell-Garnett effective medium approximation model. Due to the photoluminescence properties of nc-Si embedded in Si3N4 matrix, the TL-ARC has the inherent capability of down-converting ultraviolet photons to low-energy photons that are useful to Si solar cells. The deposition of the TL-ARC on Si solar cell is fabricated with plasma enhanced chemical vapor deposition in a single process step. The performance enhancement of Si solar cells by the TL-ARC has been demonstrated by experiments.