Design and modeling of a planar 2D nanostructured intermediate layer for light management in a very-thin SHJ bottom cell based monolithic perovskite/silicon tandem solar cell

We present an optical simulation for a very-thin (60 μm) SHJ (silicon heterojunction cell) bottom cell based planar monolithic perovskite/silicon tandem solar cell incorporated with an intermediate reflector layer (IRL) in between the top and the bottom sub-cell to study the light management. The simulation was performed in a commercial software called Ansys Lumerical FDTD Solver. In this study, the tandem solar cell was simulated by incorporating a TFOR (topologically flat but optically rough) IRL of different periods, a DBR (distributed Bragg reflector) IRL, and a combination of (TFOR + DBR) IRL in the intermediate region to check the optical absorptance enhancement in the top and the bottom sub-cells, and, also the reflectance spectrum of the tandem solar cell. The tandem solar cell incorporated with a TFOR IRL was simulated for a range of top cell thicknesses, keeping the bottom cell thickness 60 μm (fixed); aiming to use as a flexible tandem solar cell. This exhibits a current density (Jsc) enhancement in the bottom sub-cell due to the incorporation of TFOR IRL, with a maximum for 500 nm period TFOR. However, the current density of the top sub-cell remains unchanged. The closest Jsc of both the top and the bottom sub-cells reaching the current-match condition is found in the tandem solar cell incorporated with a 500 nm period TFOR IRL. For the PIN based perovskite (500 nm)/silicon (60 μm) tandem solar cells, the maximum current density enhancement in the bottom sub-cell resulting from the incorporation of a 500 nm period TFOR IRL is 0.43 mA/cm2 . However, a DBR IRL or (TFOR + DBR) IRL incorporation in the tandem solar cell could not improve the current density of the bottom sub-cells. Instead, it increases the current density in the top sub-cells. Moreover, a current density loss was also analyzed in the TFOR IRL which shows that the current density loss decreases by increasing the TFOR period and a maximum loss is at 200 nm period. Further, an electric field analysis was also done in the top and the bottom sub-cells at peak absorption wavelengths, which shows that the electric field is more concentrated in the bottom sub-cell due to TFOR IRL, confirming the forward scattering of light in the tandem solar cell incorporated with TFOR IRL.