The performance of lead halide perovskite optoelectronic devices continues to improve, yet the efficiencies are still well below the radiative limit. To approach the radiative limit, detailed understanding of impurities/defects and precise control over their concentrations are required. In Part I, we demonstrated that the soft Lewis acidity of Pb2+ induces a chemical reaction between PbI2 and aliphatic amines producing Pb-alkylamide bonds which can be subsequently incorporated into thin films. Here, we investigate the consequences of these impurities in methylammonium lead triiodide (MAPbI3) thin films. In particular, we link Pb-alkylamide impurities to an extrinsic degradation pathway resulting in Pb0 formation. The proposed mechanisms proceeds via β-C-H proton transfer reactions of the amido Pb species. Metallic Pb+/Pb0 defects acting as non-radiative recombination centers may limit the performance of many perovskite layers. However, optimal concentrations of Pb-methylamide impurities in sub-stoichiometric (slight excess of PbI2) MAPbI3 films passivate Pb0 defect formation, shown here to simultaneously correlate to improvements in photoluminescence lifetime. These results elucidate the beneficial properties of Pb-amide impurities in low concentrations and the sensitivity of halide perovskite materials to extrinsic defect chemistry.
All Science Journal Classification (ASJC) codes
- Materials Chemistry