This talk has been part of the HOPV22 conference that took place in Valencia.
Halide perovskite semiconductors are generating enormous excitement for next-generation photovoltaics in both single junction and tandem device forms. Their performance is striking given that these absorber layers are rife with heterogeneity on the nanoscale in their structural, chemical and optoelectronic properties. Here, I will delve into these nanoscale features by presenting recent works employing multimodal microscopy techniques to understand relationships between these properties, and their link to device performance and stability. I will give examples where we find the heterogeneity beneficial for performance, where chemical heterogeneity is able to funnel charge carriers away from deep traps . However, nanoscale trap clusters are present in these absorbers that act as unwanted non-radiative recombination sites  and sites of instability (arXiv:2107.09549) — and thus must be removed. These trap clusters relate to phase impurities  and form in regions that are not stabilised by octahedral tilt . This interplay between the good, the bad and the ugly — and appropriate management of these effects — will dictate commercial prospects of these promising technologies.