Interplay of Kinetic and Thermodynamic Reaction Control Explains Incorporation of Dimethylammonium Iodide into CsPbI₃

Abstract

CsPbI 3 is a promising material for optoelectronics owing to its thermal robustness and favorable bandgap. However, its fabrication is challenging because its photoactive phase is thermodynamically unstable at room temperature. Adding dimethylammonium (DMA) alleviates this instability and is currently understood to result in the formation of DMA x Cs 1– x PbI 3 perovskite solid solutions. Here, we use NMR of the 133 Cs and 13 C local structural probes to show that these solid solutions are not thermodynamically stable, and their synthesis under thermodynamic control leads to a segregated mixture of yellow one-dimensional DMAPbI 3 phase and δ-CsPbI 3 . We show that mixed-cation DMA x Cs 1– x PbI 3 perovskite phases only form when they are kinetically trapped by rapid antisolvent-induced crystallization. We explore the energetics of DMA incorporation into CsPbI 3 using first-principles calculations and molecular dynamics simulations and find that this process is energetically unfavorable. Our results provide a complete atomic-level picture of the mechanism of DMA-induced stabilization of the black perovskite phase of CsPbI 3 and shed new light on this deceptively simple material.

A Complete Picture of Cation Dynamics in Hybrid Perovskite Materials from Solid-State NMR Spectroscopy

“…Having demonstrated this relaxometry methodology for MA + , FA + , and GUA + , we note that it can be readily extended to understand the dynamics of other relevant cations used in hybrid perovskites, such as dimethylammonium (DMA + ) − and methylenediammonium (MDA + ). , We further highlight that by understanding the FA + cation dynamics, we were recently able to mitigate the detrimental 1 H relaxation by deuteration and enable dynamic nuclear polarization experiments that show the structure of a surface coating on a single thin film . Overall, the complete picture of the cation dynamics presented here will help reveal the underlying causes of the beneficial optoelectronic properties seen in some hybrid perovskite formulations and thereby aid the design of perovskite solar cells with higher efficiencies in the future.…”

The race between complicated multiple cation/anion compositions and stabilization of FAPbI3 for halide perovskite solar cells

“…It is conceivable that under specific growth conditions, for example, controlled by growth kinetics, the speciation of that cation could be affected. Mishra et al have recently shown this to be the case for Cs/dimethylammonium lead iodide perovskites 64 . In this context, two studies are noteworthy.…”

“…Mishra et al have recently shown this to be the case for Cs/dimethylammonium lead iodide perovskites. 64 In this context, two studies are noteworthy. Usiobo et al have used nanoscale mass spectrometry imagining to study Cs, K, and Rb doped hybrid halide perovskites and found that, while Rb preferentially occupies grain boundaries as an Rb-rich, non-perovskite phase, there is also a detectable Rb signal originating from the perovskite grains.…”

Cs1−xDMAxPbI3versus CsPbI3for Perovskite Solar Cells

“…The fourth phase is a yellow photoinactive polymorph referred to as the δ‐phase, [ 40,41 ] which unfortunately is the thermodynamically stable CsPbI 3 phase at room temperature. [ 42 ] There is, however, a clear peak shift, where the dominant XRD peaks for the perovskite phase are shifted to higher diffraction angles for the sample annealed at the higher temperature. Larger diffraction angles mean a smaller lattice spacing, which is in line with larger DMA + ions being replaced by smaller Cs + ions.…”