Surface Impurity Healing by the Formation of 1D/3D Perovskite Heterojunctions for Inverted Perovskite Solar Cells

The presence of native impurities of lead iodide (PbI 2 ) and δ-phase perovskite on the surface of solution-processed metal halide perovskite films can induce nonradiative recombination and impede charge transport and extraction. In this work, we propose a surface-impurity healing strategy using 5-(2-hydroxyethyl)-3,4-dimethylthiazolium iodide (HDI) to simultaneously eliminate detrimental PbI 2 and δ-phase perovskite impurities by converting them in situ into stable one-dimensional (1D) perovskites. This process creates a 1D/3D perovskite heterojunction at the interface, simultaneously passivating defects and optimizing the energy band alignment. As a result, the charge extraction is extremely enhanced, while the nonradiative recombination is tremendously suppressed. After HDI treatment, the power conversion efficiency (PCE) reached 25.30% with a fill factor of 84.21%. And the unencapsulated devices retained 90% of their initial PCE after 2400 h of storage in a N 2 atmosphere and approximately 80% of their initial PCE after 300 h of maximum power point tracking under one-sun illumination. In addition, mini-modules with an aperture area of 15 cm –2 using the surface impurity healing strategy also achieved a certified PCE of 21.62%. This study demonstrates the synergistic effect of surface impurity healing and interfacial engineering in simultaneously enhancing the PCE and stability of perovskite photovoltaics.