Abstarct: Increased global energy consumption and the subsequent increase in greenhouse gases have resulted in irreversible environmental pollution and damages. There has been a surge in scientific efforts to reduce global dependence on exhaustible resources and environmentally destructive fuels and move towards affordable renewable energies. Among them are the efforts focused on producing electrical energy from sunlight with semiconductors. The present investigation is an attempt to study and improve the performance of solar cells with Graphene/ Gallium Arsenide baxsed Schottky junctions. This solar cell is composed of three laxyers, the Gallium Arsenide substrate, Silicon Oxide and Graphene. In order to obtain cell performance parameters, the solar cell is simulated with Silvaco software. The important cell parameters include open-circuit voltage (V_OC), short-circuit current (I_SC), fill factor (FF) and power conversion efficiency (PCE). Simulation results By examining the effects of substrate thickness, transparency and number of graphene laxyers show that the best power conversion efficiency for the solar cell with 3- laxyers graphene and 4 micrometer Gallium Arsenide substrate is approximately 1.196%. To improve the efficiency of the solar cell, We simulated rectangular and trapezoid nano-grating on the cell and we were able to increase the cell's efficiency by about 2.05% . Then reduced the height of the grating to match the graphene and GaAs, and applied rectangular and trapezoid grating. In this case, the efficiency in a rectangular nanotubes was estimated to be 1.8 % and in a trapezoid about 1.9%.