Abstract:
Wide bandgap perovskite solar cells are becoming the preferred choice for top cells in a tandem architecture with crystalline silicon solar cells. This is due to their bandgap tunability (1.6 to 3eV), low-temperature solution processing, fast charge carrier rate, long carrier diffusion length, and high absorbance in the visible region. Among the wide bandgap perovskites, a mixed cation, mixed halide composition containing CsxFA1-xPbI3-yBry has is a popular choice because the presence of Br widens the bandgap and the addition of Cs stabilizes the crystal structure. However, these perovskite layers were fabricated using a one-step spin-coating technique even though sequential deposition promotes crystallization and offers bbetter film coverage. In this paper, we have fabricated a Cs0.2FA0.8PbI3-xBrx perovskite absorber layer using sequential deposition. The concentration of Br was varied from 0 to 1, and the optical, structural and morphological properties of the film were studied. As the concentration of Br was increased, the perovskite showed better crystallinity however, beyond Br-0.3, the presence of another perovskite phase matching CsPbBr3 was detected owing to a preference for the Pb-Br over the Pb-I complex. Optically, the perovskite films also skewed from the predicted bandgap for Br concentrations of 0.5 and 0.7. Their bandgap was in the 2 eV range, which also matches with CsPbBr3. The morphology showed the presence of large grains with high surface roughness. This study explores compositional tuning via the sequential deposition route for a wide bandgap perovskite absorber layer.
