Nitrogen Soaking Promotes Lattice Recovery in Polycrystalline Hybrid Perovskites

On the basis of experiment and theory, a general paradigm is drawn that reconsiders N2 not simply being an inert species but rather an effective healing gas molecule if entering a methylammonium lead iodide (MAPbI3) layer. Nitrogen is soaked into polycrystalline MAPbI3 via a postdeposition mild thermal treatment under slightly overpressure conditions to promote its diffusion across the whole layer. A significant reduction of radiative recombi- nation and a concurrent increase of light absorption, with a maximum benefit at 80 °C, are observed. Concomitantly, the current of holes drawn from the surfaces with nanometer resolution through a biased tip is raised by a factor of 3 under N2. This is framed by a reduction of the barrier for carrier extrac- tion. The achieved improvements are linked to a nitrogen-assisted recovery of intrinsic lattice disorder at the grain shells along with a simultaneous stabilization of undercoordinated Pb2+ and MA+ cations through weak electro- static interactions. Defect mitigation under N2 is reinforced in comparison to the benchmark behavior under argon. It is additionally unveiled that surface stabilization through N2 is morphology-independent and thus can be applied after any preparation procedure. Such simple and low-cost strategy can com- plement other stabilizing solutions for perovskite solar cells or light-emitting diode engineering.