This study compares the electrical output of photovoltaic (PV) cells encapsulated with silicones having different refractive indices to unencapsulated PV cells. It is demonstrated that the optical concentration ratio of dome-shaped concentrator PV systems can be increased by using a higher refractive-index encapsulant. The short-circuit photocurrent of the PV cell having high-refractive-index encapsulation (n=1.57) is 71% higher than that of the PV cell having a low-refractive-index encapsulation (n=1.41), and 316% higher than that of the unencapsulated PV cell. These experimental concentration-ratio enhancements are consistent with the theoretical estimates of concentration ratio dependence on the refractive index of the PV concentrator.