Controlling Phase Transitions in Two-Dimensional Perovskites through Organic Cation Alloying

Abstract

We demonstrate control over the phase transition temperature of Ruddlesden–Popper two-dimensional (2D) perovskites by alloying alkyl organic cations of varying lengths. By blending hexylammonium with pentylammonium or heptylammonium cations in different ratios, we continuously tune the phase transition temperature of 2D perovskites from approximately 40 to −80 °C in both crystalline powders and thin films. Correlating temperature-dependent grazing incidence wide-angle X-ray scattering and photoluminescence spectroscopy, we also demonstrate that the phase transition in the organic layer couples to the inorganic lattice, impacting PL intensity and wavelength. We take advantage of changes in PL intensity to image the dynamics of this phase transition and show asymmetric phase growth at the microscale. Our findings provide the necessary design principles to precisely control phase transitions in 2D perovskites for applications such as solid–solid phase change materials and barocaloric cooling.

Spectrally Stable Deep-Blue Light-Emitting Diodes Based on Layer-Transferred Single-Crystalline Ruddlesden–Popper Halide Perovskites

“…One of the major factors limiting the performances of RPP-based PeLEDs has been Joule heating during continuous device operation. At elevated temperatures, the PLQY of the single-crystalline RPP layer can be reduced as reported in previous studies in polycrystalline RPP films. , To estimate the PLQY of the single-crystalline RPP at elevated temperatures, temperature-dependent PL of a bulk PEA 2 MAPb 2 Br 7 RPP single crystal was measured. The temperature of the RPP sample was gradually elevated from room temperature to 373 K, followed by cooling back to 313 K. As shown in Figure c, a significant reduction in PL peak intensity was measured, showing a nearly 3-fold decrease in the intensity between room temperature and 313 K. At temperatures above 353 K, a broad secondary peak appeared at nearly 500 nm accompanied by a broadening of the line width of the main peak (see Figure d), conceivably as a result of structural dynamics of the RPP lattice brought on by tilting of the [PbBr 6 ] 4– octahedral or the phase transition. ,, It is noteworthy that an almost full recovery of the PL peak intensity at approximately 445 nm was made during the cooling process.…”

Smallest Organic Spacers-Based Ruddlesden–Popper and Dion–Jacobson Perovskites: Which One Is Better for Optoelectronics?

“…As a consequence, for higher n -value ( n = 4) DJ perovskites, the heat absorption occurred at relatively lower temperature (∼97 °C). It should be noted that for n = 4, a highly intense peak at low temperature (∼43 °C) is also observed which corresponds to the phase transition of bulk perovskite, i.e., MAPbI 3 , and for the remaining quasi and pure 2D phases ( n = 1 to 4), the phase transition occurred at higher temperatures, which shows that, compared to the bulk, the DJ-EDA perovskites are thermally stable . For comparison, we have also added the DSC curve for the n = 2 RP-EA, which has shown the phase transition temperature at ∼89 °C, which is lower than its counterpart n = 2 DJ-EDA (Figure S5b).…”

“…It should be noted that for n = 4, a highly intense peak at low temperature (∼43 °C) is also observed which corresponds to the phase transition of bulk perovskite, i.e., MAPbI 3 , and for the remaining quasi and pure 2D phases (n = 1 to 4), the phase transition occurred at higher temperatures, which shows that, compared to the bulk, the DJ-EDA perovskites are thermally stable. 47 For comparison, we have also added the DSC curve for the n = 2 RP-EA, which has shown the phase transition temperature at ∼89 °C, which is lower than its counterpart n = 2 DJ-EDA (Figure S5b). In order to determine the photocurrent response of the RP-EA and DJ-EDA perovskites, a lateral photodetector prototype (FTO/perovskite/FTO), see device configuration schematics in Figure 6a, is fabricated by making a uniform scratch on a FTO coated glass substrate using a diamond cutter tool followed by substrate cleaning steps.…”

Multichromism in Halide Perovskites

“…On the other hand, in the HA 2 PbI 4 , (Hexylammonium, HA), the reversible phase transition is observed by the rearrangement of A′ cation as studied by the Differential Scanning Calorimetry (DSC) analysis (Figure 5c,d). [ 89 ] The rearrangement of HA in HA 2 PbI 4 single crystals over cooling and heating cycles allows alternation of H‐bonds with octahedral. Furthermore, reversible chemical transformation depicts the alteration of the A′ cation when the I 2 molecule is introduced in HA 2 PbI 4 2D perovskite [ 90 ] as shown in Figure 5e.…”