Methylammonium iodide and its effect as an intrinsic defect in perovskites structure and device performance

• •

  The perovskite framework best serves the stoichiometric ratios of precursors.

  •

  Excess organic cations in the perovskite results in non-excitonic characteristics.

  •

  Excess halides change crystallinity and photoluminescence response in perovskite.

  •

  Excess halides introduce reliability issues in perovskite-based photodetectors.

  Abstract

  Organo-metal halides are the new generation of functional materials formed on a perovskite  framework, ABX3. Despite the high throughput of these semiconductors, they are prone to long-term degradation. A degradation process that is still far from understood. This might be attributed to the complex nature of the organic compound in the A site of the perovskite structure. In this work, we disturb the perovskite structure, methylammonium  lead iodide  (CH3NH3PbI3), by inducing intrinsic defects in it using different ratios of the precursors. The presence of excess CH3NH3I (MAI) creates vacancies in the structure, resulting in higher degrees of crystallization and lower decomposition rate. The deviations from the norm in the crystalline lattice highlight the role of MAI in the degradation process. Depending on the concentration, excess MAI may also liberate halide ions. These halide ions then act as dopants  and change the bandgap of the perovskite semiconductors. The dark current density in the photodetectors fabricated based on these materials increases from 10−12 to 10−8 Acm−2, as the concentration of MAI in the perovskite decreases, with the exception of the base concentration. However, MAI possess a disordered molecular structure which may result in formation of trap vacancies. Therefore, the concentration of MAI in the perovskite structure must be adjusted such that formation of [PbI6(CH3NH3) n]m clusters are possible.

•