Efficient Formamidinium-Based Planar Perovskite Solar Cells Fabricated Through CaI2-PbI2 Precursor

The performance of perovskite solar cells (PSCs) is sensitive to the quality of perovskite films. Sequential deposition enabling the controlled growth of film is promising to obtain high-quality perovskite films. However, it is challenging to fabricate formamidinium-based planar PSCs via sequential deposition, mainly due to the small penetration depth of the large size formamidinium cation into a compact PbI2 film during perovskite formation. Here, CaI2 is introduced into PbI2 precursor solution, which brings two benefits. First, the porous low-crystalline CaI2-PbI2 film results in reduced local nucleation sites and improved perovskite conversion, leading to perovskite films with high crystallinity and larger grains. Second, the residual CaI2 existed at the surface and grain boundaries of the perovskite films can passivate the detrimental crystal defects. Solar cells based on CaI2-PbI2 precursor demonstrate high open-circuit voltage (Voc) up to 1.14 V and improved power conversion efficiency (PCE) of more...