Sequentially Deposited Compact and Pinhole-Free Perovskite Layers via Adjusting the Permittivity of the Conversion Solution

The preparation of compact and pinhole-free absorber layers is a major step towards device reproducibility and high performance for planar organic-inorganic perovskite solar cells. It is well known that the sequential deposition method exhibits some advantages over the common one-pot synthesis in terms of controlling the surface coverage. However, it still miscarries to produce pinhole-free layers from solution, mainly due to the occurrence of dissolution and recrystallisation processes. We show that by a careful choice of the permittivity of the alcoholic solvent in the conversion step the surface morphology can be finely modified, thereby yielding pinhole-free and compact absorber films comparable to that from vapour-assisted solution techniques. It is observed that the permittivity controls the intensity of the Ostwald ripening effect and that a low value of the former enables an in situ intercalation of precursor materials into the lead halide framework. We successfully prepared smooth and mirror-like perovskite surfaces that demonstrate enhanced optoelectronic properties and photovoltaic performance compared to films from the native two-step deposition in isopropanol. This strategy provides a facile approach for obtaining high-quality layers in the planar architecture by simple solution processing.