Trans-polyacetylene doped Cs2AgBiBr6: Band gap reduction for high-efficiency lead-free double perovskite solar cells

This study introduces an innovative approach involving the synthesis of lead-free halide double perovskite (LFHDP) solar cell Cs2AgBiBr6 and that with the doping of trans-polyacetylene (t-PA) via the sol–gel method. Through X-ray diffraction (XRD) analysis, we confirm the cubic structure and, in addition, an observable growth in grain size attributed to t-PA doping. A comprehensive exploration of optical parameters, including band gap, refractive index, electronegativity, extinction coefficient, and dielectric constant was conducted through UV–Vis spectrophotometry. The pristine Cs2AgBiBr6 exhibited a band gap energy (Eg) of 1.9 eV, while with t-PA doping the Eg decreased to 1.84 eV, indicating a notable enhancement in light absorption. The calculated optical electronegativity is 0.49 which suggests a shift towards a more covalent nature. The J-V curve shows parameters for pristine thin film as Jsc of 5.13 mA/cm2, Voc of 0.92 V, FF of 0.69, and the efficiency of 3.29 %. On the other hand, the t-PA doped thin film exhibits improvement of the parameters which are Jsc of 5.7 mA/cm2, Voc of 0.929 V, and FF of 0.75, leading to a significantly elevated efficiency of 3.98 %. This enhanced efficiency is 20.97 % higher than that of the pure Cs2AgBiBr6, clearly showing an uplifted performance. In addition to the experiment, computational method based on finite difference time domain technique was used to check the stability of the material. The study shows the mechanical and dynamical stability of the Cs2AgBiBr6.