2D PEA₂PbI₄–3D MAPbI₃ Composite Perovskite Interfacial Layer for Highly Efficient and Stable Mixed-Ion Perovskite Solar Cells

Progress toward perovskite solar cells (PSCs) with higher efficiency and stability requires further enhancing the light absorption, reducing the carrier recombination at defects and interfaces, improving the charge carrier separation, and minimizing the energy loss crossing the interfaces. Interface passivation and device structure optimization are the main strategies to improve efficiency and device stability. In this work, we report a simple method to combine the two strategies, i.e., realize the pervoskite heterostructure and the passivation layer simultaneously in a single two-dimensional (2D) PEA2PbI4–three-dimensional (3D) MAPbI3 composite perovskite interfacial layer. We use a mixed solution of methylammonium iodide (MAI) and phenethylammonium iodide (PEAI) to react with the intentionally introduced excess PbI2 in the Cs0.05(MA0.15FA0.85)0.95Pb(I0.85Br0.15)3 (CsMAFA) perovskite layer and form the MAPbI3/CsMAFA heterostructure and the 2D PEA2PbI4 perovskite passivation layer. Systematic investigations show that the MAPbI3/CsMAFA heterostructure can enhance the light absorption and the charge carrier separation at the interfaces, and thus improve the short-circuit current (Jsc) of solar cells. The 2D PEA2PbI4 perovskite layer can effectively passivate the interfacial defects and improve the fill factor (FF) and open-circuit voltage (Voc). The working mechanisms of MAI and PEAI treatment are also discussed. This work offers a promising path for the fabrication of highly efficient and stable PSCs.