Perovskite nanocrystal superlattices (NC SLs), made from
millions
of ordered crystals, support collective optoelectronic phenomena.
Coupled NC emitters are highly sensitive to the structural and spectral
inhomogeneities of the NC ensemble. Free electrons in scanning electron
microscopy (SEM) are used to probe the cathodoluminescence (CL) properties
of CsPbBr3 SLs with a ∼20 nm spatial resolution.
Correlated CL-SEM measurements allow for simultaneous characterization
of structural and spectral heterogeneities of the SLs. Hyperspectral
CL mapping shows multipole emissive domains within a single SL. Consistently,
the edges of the SLs are blue-shifted relative to the central domain
by up to 65 meV. We discover a relation between NC building block
colloidal softness and the extent of the CL shift. Residual uniaxial
compressive strains accompanying SL formation are contributors to
these emission shifts. Therefore, precise control over the colloidal
softness of the NC building blocks is critical for SL engineering.