Metal Defects in MAPbI₃ Perovskites: Uncovering the Roles of Ni, Cu, Ag, and Au

In perovskite solar cells, understanding how transition metals penetrate the perovskite layer and affect its degradation and optoelectronic properties is crucial for designing more stable devices. Here, we combine experiments and density functional theory to investigate the interaction of Ni, Cu, Ag, and Au with MAPbI₃. Our simulations show that Au and Ni spontaneously incorporate into MAPbI₃, as revealed by their negative formation energies. Although Au, Cu, and Ag prefer interstitial configurations, Au behaves distinctly, indicating that the atomic radius plays a more decisive role than the valence configuration. Ni, in turn, preferentially substitutes Pb sites without introducing midgap states despite its partially filled 3d shell. Experimentally, X-ray photoelectron spectroscopy, current-voltage measurements, and UV-vis absorption reveal that all metals diffuse into MAPbI₃, but only Ag and Cu form semiconductor halide phases that degrade device performance. In contrast, Au and Ni migrate without compromising optical absorption or charge transport, consistent with theoretical predictions. In general, these results highlight Au and Ni as promising contact materials for perovskite solar cells, as their incorporation avoids detrimental electronic or radiative effects compared to other metals.