Absorption Enhancement in Perovskite based Thin Film Solar Cells using Whispering Gallery Modes of Dielectric Spheres

Organic and inorganic halide perovskite solar cells (PSC) are regarded as a promising candidate for next-generation photovoltaic technology owing to their low-fabrication methods and higher power conversion efficiency. PSC devices with adequate trapping of incident light, have been proposed in two different novel configurations. One with the inclusion of pristine TiO₂ microspheres and the other with CsPbI₃ coated TiO₂ microspheres, exhibiting resonating whispering gallery modes (WGM). The absorption in the CsPbI₃ active layer is enhanced due to the presence of WGM microspheres. The incoming electromagnetic wave couples with TiO₂ microsphere and forms confined resonating modes. Since, the in-coupling element is lossless, energy stored in microspheres is absorbed efficiently by the underlying active perovskite material. Thus, the devices show a higher current density in the range of <b>25 mA/cm²</b>, which is almost <b>50%</b> more than a conventional PSCs device. The performance of the designed PSCs have been tested numerically using 3D full-field finite difference time-domain (FDTD) simulation tool. Further, different designs have been discussed for deciding the appropriate position of WGM spheres w.r.t thin-film PSCs featuring back-reflector and optimized anti-reflecting coating. We have also studied the influence of multi-sized array of spheres as well as perovskite coated dielectric spheres to propose an analytical model based on temporal coupled mode theory.