Multidimensional coherent spectroscopy reveals triplet state
coherences in cesium lead-halide perovskite nanocrystals

Advanced optoelectronics require materials with newly
engineered characteristics. Examples include a class of materials
named metal-halide perovskites that have tremendous significance to
form perovskite solar cells with photovoltaic efficiencies. Recent
advances have also applied perovskite nanocrystals in
light-emitting devices. The unusually efficient light emission of
cesium lead-halide perovskite may be due to a unique excitonic fine
structure made of three bright triplet states that minimally
interact with a proximal dark singlet state. Excitons are
electronic excitations responsible for the emissive properties of
nanostructured semiconductors, where the lowest-energy excitonic
state is expected to be long lived and hence poorly emitting (or
‘dark’).