Investigation into the Photoluminescence Red Shift in Cesium Lead Bromide Nanocrystal Superlattices

The formation of cesium lead bromide (CsPbBr₃) nanocrystal superlattices (NC SLs) is accompanied by a red shift in the NC photoluminescence (PL). The values of the PL red shift reported in the literature range from none to ∼100 meV without unifying explanation of the differences. Using a combination of confocal PL microcopy and steady-state optical spectroscopies we found that an overall PL red shift of ∼96 meV measured from a macroscopic sample of CsPbBr₃ NC SLs has several contributions: ∼ 10-15 meV from a red shift in isolated and clean SLs, ∼ 30 meV from SLs with impurities of bulklike CsPbBr₃ crystals on their surface, and up to 50 meV or more of the red shift coming from a photon propagation effect, specifically self-absorption. In addition, a self-assembly technique for growing micron-sized NC SLs on the surface of perfluorodecalin, an inert perfluorinated liquid and an antisolvent for NCs, is described.