Ligand-Mediated Surface Reaction for Achieving Pure 2D Phase Passivation in High-Efficiency Perovskite Solar Cells

The surface passivation with the heterostructure of the 2D/3D stack has been widely used for boosting the efficiency of n-i-p perovskite solar cells (PSCs). However, the disordered quantum well width distribution of 2D perovskites leads to energy landscape inhomogeneity and crystalline instability, which limits the further development of n-i-p PSCs. Here, a versatile approach, ligand-mediated surface passivation, was developed to produce a phase-pure 2D perovskite passivation layer with a homogeneous energy landscape by dual-ligand codeposition. The preferential adsorption of 3,6-dimethyl-carbazole-9-ethylammonium iodide with a large molecular size and lower adsorption energy could regulate the surface reaction between the m-fluorophenylethylammonium iodide and perovskite surface, resulting in a 2D perovskite with a narrow quantum well distribution and a uniform surface potential distribution. Beyond this, the preservation of the surface-confined 2D passivation layer retained a higher electric field at the interface of perovskite and the hole transport layer. As a result, the champion device reached an efficiency of 25.86% for the 0.05 cm² device and 25.08% for the 1 cm² device, with enhanced operational stability (T₉₀ > 1000 h) and much better thermal stability. Our work provides deeper insights into efficient and stable 2D passivation for PSCs.