In this paper, a 3D finite element method (FEM) technique is exploited to simulate a planar perovskite solar cell. To fully characterize the proposed device, combined optical-electrical modeling method is used. The presented model is validated through comparisons with experimental work. A new structure is introduced which includes a layer of CH3NH3SnI3 as a second absorber layer in the perovskite solar cell (PSC) structure based on CH3NH3PbI3. In this new structure, power conversion efficiency (PCE) is increased from 14.32% to 15.32% when the thickness of CH3NH3SnI3 is 200 nm. The short circuit current (J(sc)) is improved by coating 40 nm MgF(2 )layer which act as an anti reflector layer on the surface of the presented PSC. The influence of periodically corrugated back and anti reflector on the presented PSC is considered. As a result of replacing a flat back and anti reflector layer with periodically corrugated back and anti reflector layer, respectively, the PCE of this new proposed PSC structure with two active layers reaches 17.5%.