Enhancing Efficiency of Lead-Free Cs2TiIxBr6-x Perovskite Solar Cells Through Linear and Parabolic Grading Strategies: Toward 31.18% Efficiency

The most amazing environmentally friendly energy source is solar energy, which can be captured with the aid of photovoltaic (PV) cells. Perovskite solar cells (PSCs) that are hybrid (organic–inorganic) have demonstrated remarkable PV ability. The advantages of halide-based perovskite are numerous and include cheap cost, high efficiency, and simplicity in fabrication. Due to their poisonous nature, lead (Pb)-based PSCs often pose a concern to the environment. They also have other drawbacks, such as stability problems, problems with scalability, and health risks associated with Pb exposure. Thus, the primary intent of this study is to examine the Pb-free, inorganic titanium-based perovskite complex Cs₂TiI_xBr_6-x, which serves as the active layer. When compared with other elements, titanium is nontoxic, strong, affordable, and easily accessible. To improve the efficiency of lead-free (Au/CuSbS₂/Cs₂TiI_xBr_6-x/CdS/FTO) device structure, both linear and parabolic grading methods are used in the simulation. The perovskite composition Cs₂TiI_xBr_6-x is a mixed halide system, with different amounts of iodine (I) and bromine (Br) ions integrated into the crystal lattice. Within the halide system, “x” indicates the percentage of iodide ions that replace bromide ions. Light absorption and energy conversion efficiency in solar cells may be maximized by fine tuning the material's band gap by varying “x,” which can range from 0 to 6. When the active layer is graded linearly, the band gap is adjusted by adjusting the composition x, which ranges from 0 to 6, throughout the active layer's thickness. The bending factor changes from 0 to 1 in the case of parabolic grading of the Cs₂TiI_xBr_6-x layer, indicating an enhancement in the device's PCE as a result of high wavelength photon absorption. Our simulations show a significant improvement in PCE, with an astounding result of 31.18% for parabolic grading, a 7.93% increase above PCE from linear grading, which is 28.89%. Other noteworthy metrics that exhibit exceptional outcomes include J_SC 34.36 mA.cm⁻², FF 86.81%, and V_OC 1.0452 V. The stability in the output of the device in the realistic temperature range confirms the highly stable nature of the proposed PSC device. These results show how effectively our approach improves the efficiency and effectiveness of Pb-free PSC's. As we are interested in this realistic environmental temperature range of the whole world, we proposed that Cs₂TiI_xBr_6-x-based PSCs are highly suitable and stable for the real-time experiment, which is the need of PSCs nowadays.