Dimethylammonium: An A‐Site Cation for Modifying CsPbI₃

Abstract

All-inorganic perovskite materials are attractive alternatives to organic-inorganic perovskites because of their potential for higher thermal stability. Although CsPbI 3 is compositionally stable under elevated temperatures, the cubic perovskite α-phase is thermodynamically stable only at >330 C and the low-temperature perovskite γ-phase is metastable and highly susceptible to nonperovskite δ-phase conversion in moisture. Many methods have been reported which show that the incorporation of acid (aqueous HI) or "HPbI 3 "-recently shown to be dimethylammonium lead iodide (DMAPbI 3)-lowers the annealing temperature required to produce the black, perovskite phase of CsPbI 3. Herein, the optical and crystallographic data presented show that dimethylammonium (DMA) can successfully incorporate as an A-site cation to replace Cs in the CsPbI 3 perovskite material. This describes the stabilization and lower phase transition temperature reported in the literature when HI or HPbI 3 is used as precursors for CsPbI 3. The Cs-DMA alloy only forms a pure-phase material up to %25% DMA; at higher concentrations, the CsPbI 3 and DMAPbI 3 begin to phase segregate. These alloyed materials are more stable to moisture than neat CsPbI 3 , but do not represent a fully inorganic perovskite material.

Chemical and Structural Degradation of CH3NH3PbI3 Propagate from PEDOT:PSS Interface in the Presence of Humidity

“…A redshift in the PL emission has been observed in mixed‐cation Cs x [(CH 3 ) 2 NH 2 ] 1− x PbI 3 perovskites with increasing content of the larger (CH 3 ) 2 NH 2 + cation (when x ≤ 0.2) due to consequent changes in the crystal structure that increase orbital overlap between Pb and I atoms. [ 16 ] We note a secondary emission at 828 nm in the PL measurements when light is incident on the film and glass sides of the perovskite made on PEDOT:PSS between days 0–2 (Figure 2B). We believe this secondary emission stems from the self‐absorption of the primary emission as a result of internal reflections.…”

Strategies for highly efficient and stable cesium lead iodide perovskite photovoltaics: mechanisms and processes

“…Marshall and coworkers further explored and quantified the impact and limitations of the production method of DMA + partially replacing Cs + . 72 They found that the perovskite could form a stable phase only when 25% DMA + replaced Cs + . When the concentration of DMA + increased, significant phase separation (CsPbI 3 and DMAPbI 3 ) occurred.…”

Mechanism of the Dimethylammonium Cation in Hybrid Perovskites for Enhanced Performance and Stability of Printable Perovskite Solar Cells

“…[ 17 ] Snaith et al presented that DMA can successfully incorporate into the CsPbI 3 perovskite to form an alloyed composition of Cs x DMA 1− x PbI 3 , which is more stable under atmospheric conditions than original CsPbI 3 . [ 18 ] In such a broad research background, some publications have revealed that DMA can successfully incorporate in the CsPbI 3 films after mild annealing. However, there have been conflicting reports deem that it simply manipulates the crystallization process and then serves as a bystander in the final films.…”