β-Alanine-Anchored SnO₂ Inducing Facet Orientation for High-Efficiency Perovskite Solar Cells

SnO₂ films as a promising electron transport layer (ETL) have been widely used in planar-type perovskite solar cells to achieve an impressive improvement in the conversion efficiency. However, compared with a mesoporous ETL, the interfacial charge carrier transfer of the SnO₂ ETL is severely limited due to the issues of oxygen vacancy defects and crystal lattice mismatch between SnO₂ and the perovskite, which generally leads to the growth of randomly stacked and porous perovskite layers and subsequently impacts the charge transport and transfer properties. In this work, we developed a facile approach by inducing a bifunctional molecule, β-alanine, into the SnO₂ ETL, which can serve as a bridge to modulate the interfacial charge transfer and the perovskite crystallization kinetics. Benefited by the interfacial β-alanine, we grew a highly orientational perovskite layer that exhibited superior charge transport properties. Meanwhile, the β-alanine caused an intimate connection between the perovskite and SnO₂ to enhance the interfacial charge transfer. As a result, the power conversion efficiency (PCE) of the β-alanine-modified device achieved a much-improved value of 19.67% and showed high reproducibility. This work provides a way for developing a high-performance ETL toward the scalable fabrication of highly efficient PSCs.