Effect of various interlayers on the performance of cesium formamidinium lead mixed halide (CsFAPbX3) – Formamidinium tin iodide (FASnI3) two-terminal tandem solar cell

Abstract

In this work, 2D-Sentaurus TCAD has been used to investigate two terminal all-perovskite tandem solar cells (TSCs) having the structure Glass | ITO | PEDOT:PSS | CsFAPbX3| PCBM | Interlayer | PEDOT:PSS | FASnI3| PCBM | Ag. The thicknesses of active perovskite layers for both the bottom (FASnI3) and top (CsFAPbX3) sub-cells have been optimized for maximizing the device efficiency. Various metals (Ag, Au, Ti, Al, etc.), transparent conducting oxides (TCOs) such as ITO, FTO, and ZnO, and a polymer (PFN-Br) have been investigated for the interlayer. The dependence of solar cell performance on the thicknesses and optical constants of these interlayers, and on the angle of light incidence (θ) have been analyzed using the integrated optical generation rates. The metal-interlayer TSCs show a monotonic decrease in efficiency with increasing interlayer thickness. A 1 nm Ti-interlayer, for example, gave an efficiency of 12.9% at normal incidence. On the other hand, ITO-interlayer TSC gave its highest efficiency at an optimum interlayer thickness of 5 nm. While some of the metal-interlayer TSCs have been found to generate power for θ values up to 80°, those with more commonly used interlayers such as Ag and Au showed poor angle dependence. TSCs with all the TCO- as well as the PFN-Br- interlayers gave their highest efficiencies at oblique angles of incidence rather than at normal incidence. A peak efficiency of 12.55% was obtained at an angle of 50° for the TSC with this interlayer. To estimate the maximum amount of energy that these TSCs can generate in an year, the energy densities generated per day (Eday) were integrated and compared using the solar irradiation and temperature data from Photovoltaic Geographical Information System (PVGIS-SARAH, European Commission) database. Among all the interlayers studied here, Ti and ITO have been found to be the best metal and TCO respectively. For example, despite generating the highest short circuit current density at normal incidence, the Ag-interlayer TSC generates 79% and 82% lower energy density than these TSCs on the longest day of the year.