Nanocrystals of Lead-halide perovskites have emerged as important optoelectronic materials with excellent efficiencies in photovoltaic, light-emitting applications and as good quantum emitters with highly coherent emission. These physical properties stand in contrast with recent experimental observations of high dynamic disorder, room temperature structural transformation, and questionable material stability.

For improving our understanding, I will argue in favor of studying these materials at the limit of smallest crystals we can make. 

I will show how through morphologic control of the perovskite cesium lead halide nanocrystal; we control quantum confinement of excitons with atomic precision and tune anisotropic emission. 

In the case of 2D plates we observe increased excitonic interaction and increased absorption coefficient. In the case of nanowires, we show that the broken symmetry manifests in polarized emission which enables fabrication of highly functional films through 3D printing. In addition, by changing the anion composition facile band gap tunability at room temperature throughout the visible spectrum is achieved. 

This versatility, position colloidal perovskites as a unique model system for the study excitons at the new nanoscale material system. These lessons are important in the context of understanding and designing loss-less next generation materials for energy conversion applications and as potential single photon sources.