Photo de-mixing in mixed halide perovskites: the roles of ions and electrons

Abstract

Mixed halide perovskites have attracted great interest for applications in solar cells, light emitting diodes and other optoelectronic devices due to their tunability of optical properties. However, these mixtures tend to undergo de-mixing into separate phases when exposed to light, which compromises their operational reliability in devices (photo de-mixing). Several models have been proposed to elucidate the origin of the photo de-mixing process, including the contribution of strain, electronic carrier stabilization due to composition dependent electronic energies, and light induced ionic defect formation. In this perspective we discuss these hypotheses and focus on the importance of investigating defect chemical and ion transport aspects in these systems. We discuss possible optoionic effects that can contribute to the driving force of de-mixing and should therefore be considered in the overall energy balance of the process. These effects include the selective self-trapping of photo-generated holes as well as scenarios involving multiple defects. This perspective provides new insights into the origin of photo de-mixing from a defect chemistry point of view, raising open questions and opportunities related to the phase behavior of mixed halide perovskites.

Photo De‐Mixing in Dion‐Jacobson 2D Mixed Halide Perovskites

“…Nevertheless, this experiment suggests a critical temperature higher than 150 °C and provides a lower bound estimate of 0.07 eV for the interaction parameter Ω (Ω = T c /2R, where R is the gas constant). [39] Regarding the temperature-dependent UV-Vis experiment shown in Figure 4, XRD measurements were also taken after each temperature step to evaluate the influence of light and temperature on the film's structural properties. Compared to the XRD measurement performed on the pristine sample, we observed a decrease in peak intensity and broadening of peak width upon illumination during the first temperature step, consistent with the data in Figure 3.…”

“…Nevertheless, this experiment suggests a critical temperature higher than 150 °C and provides a lower bound estimate of 0.07 eV for the interaction parameter Ω (Ω = T c /2 R , where R is the gas constant). [ 39 ]…”

Photoinduced Segregation Behavior in 2D Mixed Halide Perovskite: Effects of Light and Heat

“…The coexistence of strain effects with other more general critical elements, such as hole and defects densities, may also play a role in approaching saturation regimes. Obtained results further suggest that the critical temperature for the photomiscibility gap (the temperature where segregation will stop) depends not only on the temperature but also on the interaction of material properties, the exposed environment, and the illumination condition …”

“…This implies that the segregation resistance cannot be evaluated by comparing the activation energies in different MHPs due to different experimental conditions, such as sample preparation methods (which would affect the grain sizes and defect levels in the samples and consequently ion migration) and illumination intensities. It has been well recognized that there are still several unanswered questions concerning PHS and that the analysis is complicated by conflicting data in the literature. , To rationalize the diverging phenomena, we investigate the PHS dependence on temperature and illumination intensity in a 2D MHP. We have developed an in situ absorption measurement to monitor the halide composition of a 2D MHP with a phenylpropylammonium (PPA) spacer under illumination.…”

“…It has been well recognized that there are still several unanswered questions concerning PHS and that the analysis is complicated by conflicting data in the literature. 31,32 To rationalize the diverging phenomena, we investigate the PHS dependence on temperature and illumination intensity in a 2D MHP. We have developed an in situ absorption measurement to monitor the halide composition of a 2D MHP with a phenylpropylammonium (PPA) spacer under illumination.…”