Ion-migration-induced dual interface dipoles for high-performance perovskite solar cells

Abstract

Low exciton binding energy and well-aligned energy levels are crucial for achieving efficient perovskite solar cells (PSCs). Here, we introduce pyridinium tetrafluoroborate (PyHBF₄) into the perovskite layer to regulate the interfaces between the perovskite and the charge transport layers effectively. This results in dual interface dipoles due to the migration of BF₄⁻, which accelerates the separation of hole-electron pairs and the extraction of carriers. Ab initio and DFT calculations, combined with various experimental characterizations, reveal that the thermodynamically favored combination of PyH⁺ and I⁻ causes BF₄⁻ to separate from the PyH⁺ cation and migrate downward along the Pb-I framework within the perovskite layer. In addition, the formation of the secondary compound PyHI on the top surface enhances cation-π interaction with Spiro-OMeTAD and increases the hydrophobicity of the perovskite film. Consequently, the PyHBF₄-treated PSCs achieve a champion efficiency of 24.93%, along with improved thermal, humidity, and operational stability.