Enhancing efficiency in double perovskite solar cells through bandgap reduction via organic polymer doping

Explanation: By Polymer doping, crystallite size is enhanced and the energy band gap is reduced as a quantum confinement concept. The films of polypyrrole (PPy) doped with Cs 2 AgBiBr 6 , lead-free halide double perovskite (LFHDP), have been synthesized through a sol–gel method. The X-ray diffraction (XRD) analysis showed the effective doping of PPy, which resulted in larger grain sizes (34 nm) and enhanced crystallinity. Optical analysis revealed the absorption in the visible region and bandgap energy (E g ) is reduced from 1.89 eV to 1.85 eV with PPy doping. The high refractive index (2.77) and absorption in the visible region due to PPy doping make it suitable for solar cell applications. The solar cells of these films have been prepared and compared to their efficiency. The structure of the solar cell is Au/Spiro-OMeTAD/Cs 2 AgBiBr 6 /TiO 2 /FTO/glass. Photovoltaic parameters of Cs 2 AgBiBr 6 solar cells with PPy doping have high open-circuit voltage (V oc ) of 0.91 V, fill factor (FF) of 0.72, short-circuit current (J sc ) of 5.37 mA/cm 2 , and efficiency (η) of 3.51 %. This study underscores the potential of PPy-doped Cs 2 AgBiBr 6 as a promising material for efficient solar energy conversion, with implications for future research in enhancing efficiency.