Nitrogen Soaking Promotes Lattice Recovery in Polycrystalline Hybrid Perovskites

• Published in: Advanced energy materials 2019-03, Vol.9 (12), p.n/a
• Main Authors: Alberti, Alessandra, Deretzis, Ioannis, Mannino, Giovanni, Smecca, Emanuele, Giannazzo, Filippo, Listorti, Andrea, Colella, Silvia, Masi, Sofia, Magna, Antonino
• Format: Article
• Language: English
• Subjects: Argon; defects; Diffusion layers; Electromagnetic absorption; Heat treatment; in situ; Lead; mitigation; Morphology; Nitrogen; Overpressure; Perovskites; Photovoltaic cells; Polycrystals; Radiative recombination; Recovery; Reduction; Solar cells; stability; Stabilization; surfaces; thermal cycle
• ISSN: 1614-6832; 1614-6840
• DOI: 10.1002/aenm.201803450

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 recombination 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 extraction. 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 electrostatic 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 complement other stabilizing solutions for perovskite solar cells or light‐emitting diode engineering. N2 proximity to MAPbI3 cations acts in mitigating the formation of defects and concurrently assists a lattice reconstruction during heating/operation. This is beneficial for the optical response of the material in absorption (spectroscopic ellipsometry) and photoemission (photoluminescence). For the same reasons, the resistance to charge extraction is reduced.