Enhancement of Quantum Efficiency in Perovskite Solar Cells Through Whispering Gallery Modes from Titanium Oxide Micro-Resonators

With the aid of 3D full-field finite difference time–domain simulations, model configurations for ${\text{CsPbI}}_3$ thin-film solar cell devices that include periodically arranged ${\text{TiO}}_2$ microspheres, exhibiting resonating whispering gallery modes (WGMs), are proposed. The ${\text{TiO}}_2$ microspheres present, either immersed in perovskite or coated with perovskite layer, between the electron- and hole-transport layers show enhanced current-conversion efficiency. The presence of WGMs lead to enhancement in the absorption of ${\text{CsPbI}}_3$ layer. The incoming electromagnetic wave couples with ${\text{TiO}}_2$ microsphere and forms confined resonating modes. Different designs are examined for deciding the appropriate position of WGM exhibiting spheres with respect to thin-film perovskite solar cell (PSC) featuring back reflector and optimized antireflectance coating. Since the incoupling element is lossless, energy stored in microspheres is absorbed efficiently by the underlying active material. This directly contributes to the increment in the current density of the solar cell. Thus, the devices show a higher current density of 23.62 mA cm⁻¹, while that in planar solar cell device shows current density of 13.68 mA cm⁻¹, for the same thickness of perovskite layer. This leads to more than 70% enhancement in the short-circuit current density than the conventional PSCs device of similar size.