Abstract
Photoinduced halide segregation in mixed halide perovskites is an intriguing phenomenon and simultaneously a stability issue. In-depth probing this effect and unveiling the underpinning mechanisms are of great interest and significance. This article reviews the progress in visualized investigation of halide segregation, especially light-induced, by means of spatially-resolved imaging techniques. Furthermore, the current understanding of photoinduced phase separation based on several possible mechanisms is summarized and discussed. Finally, the remained open questions and future outlook in this field are outlined.
Highlights
Metal halide perovskites (MHPs), as a class of unique semiconductor materials, have sparked unprecedentedly intense research activities globally over the past decade
After five minutes of electron beam irradiation, the abundance maps derived from the HRTEM images showed that the phase in the center of the nanoparticle was converted into CsPbBr3, while the phase close to the edges was in agreement with CsPb(Br0.6I0.4)3, indicating a Br/I substitution process upon electron beam exposure, consistent with previous works using PL and CL imaging techniques as discussed above [76,77,86]
By utilizing photoconductive Atomic force microscopy (AFM) coupled with PL imaging, Gomez et al [99] have revealed that photocurrent changes initiated at the grain boundaries and gradually propagated into the grain interior of the as-prepared mixed cation and mixed halide perovskite films under continuous light soaking or applied voltage, which was performed in a dry air condition with relative humidity lower than 6%
Summary
Metal halide perovskites (MHPs), as a class of unique semiconductor materials, have sparked unprecedentedly intense research activities globally over the past decade. This is mainly due to their splendid optoelectronic properties and ease of processing, enabling efficiently fabricating high-performance photovoltaic devices with low-cost. The unique crystal structure, moderate Pb-I bonding energy, and weak electrostatic interaction together with hydrogen bonding between the organic A cations and halogen anions coherently dictate MHPs featuring soft nature [27] This character makes MHPs be of easy preparation and processing, and face inherent instability issues, such as ion migration, halide segregation, phase transition and degradation [29,30,31,32,33]. The remained open questions and future outlook in this field are outlined
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