The number of studies on graphene/Si heterojunction solar cells has increased dramatically in recent years. The integration of graphene into Si photovoltaic has resulted in high power conversion efficiencies exceeding 15% in several notable applications. The need for a single compilation to discuss the issues recently discovered in the current works is necessary to help with a smooth progression and, most importantly, to understand the best direction to take when designing a high-efficiency Si-based solar cell. This article reviews and compares the remarkable findings in graphene/Si heterojunction, focusing on their photovoltaic performance indicators along with their improvement features. First, we discuss the open circuit voltage of the heterojunction and highlight the important and problematic parts. Next, the efforts to maximize the short circuit current from graphene/Si solar cells are elaborated, followed closely by the main issues in fill factor. The emphasis on power conversion efficiency is given in the following section, which is alarming for this new photovoltaic device. The article concludes with the prospect, aim and direction for graphene/Si heterojunction solar cells, along with a brief discussion regarding the potential for utilizing low-cost reduced graphene oxide in Si solar cells.