In recent years, investigation on utilizing perovskite solar cells (PSCs) has become widespread and much researches have been conducted to increase the power conversion efficiency (PCE) and sustainability of this type of solar cell. In this research, the effects of graphene (Gr) and TiO2/Gr nanocomposite as the electron transport layer (ETL) on the absorption, carriers generation and recombination, carrier transport, short-circuit current density (J(SC)), open-circuit voltage (V-OC) and PCE are investigated. For this purpose, a three-dimensional (3D) finite element method (FEM) technique is utilized. Using the monolayer Gr ETL, the absorption in the active layer enhances and J(SC) increases from 19.07 to 21.73 mA/cm(2). Meanwhile, V-OC decreases from 0.99 to 0.89 V because of the recombination at the interface of active layer and ETL. Utilizing TiO2/Gr nanocomposite as the ETL can improve carrier transport in this layer and increases V-OC from 0.99 to 1.15 V whereas J(SC) is reduced compared to the case when TiO2 was placed as the ETL. This reduction is attributed to the delivery of less light to the active layer. In the optimal case (TiO2/Gr(10%) nanocomposite), the PCE is 17.01. To further improve cell efficiency, the three HTLs CuSCN, Cu2O and NiO were placed in the cell structure and compared with each other, which the PCE of PSC yields were 17.01%, 17.81% and 17.94%, respectively. This means that the PCE has been increased by about 24%.