Grain boundary (GB) in multicrystalline silicon (mc-Si) degrades a conversion efficiency of mc-Si solar cell. To reduce the GB effect, we investigated various parameters such as the preferential GB etch, etch time, tin-doped indium-oxide (ITO) electrode, heat treatment, and emitter layer effect. Among various preferential etchants such as Sirtl, Yang, Secco, and Schimmel, a Schimmel etchant illustrated an excellent preferential etching property. We used RF magnetron sputter grown ITO film as a top contact metal. ITO films served as a top electrode as well as an effective AR coating layer. With well-fabricated mc-Si solar cells, we were able to achieve conversion efficiency as high as 16.6% at the input power of 20 mW/cm2.