Abstract
Organometal halide perovskites (OHP) are promising materials for low-cost, high-efficiency light-emitting diodes. In films with a distribution of two-dimensional OHP nanosheets and small three-dimensional nanocrystals, an energy funnel can be realized that concentrates the excitations in highly efficient radiative recombination centers. However, this energy funnel is likely to contain inefficient pathways as the size distribution of nanocrystals, the phase separation between the OHP and the organic phase. Here, we demonstrate that the OHP crystallite distribution and phase separation can be precisely controlled by adding a molecule that suppresses crystallization of the organic phase. We use these improved material properties to achieve OHP light-emitting diodes with an external quantum efficiency of 15.5%. Our results demonstrate that through the addition of judiciously selected molecular additives, sufficient carrier confinement with first-order recombination characteristics, and efficient suppression of non-radiative recombination can be achieved while retaining efficient charge transport characteristics.
Highlights
In such low-dimensional structures, besides quantum confinement, there is dielectric confinement arising from the large difference in the dielectric constants of the organic ligands (Ɛorg) and the inorganic phase (Ɛinorg)[12]
We discover that when incorporating even small concentration of an organic molecule 1,4,7,10,13,16-hexaoxacyclooctadecane as an additive we are able to suppress the crystallization of the PEABr phase and achieve an improved domain size distribution and more controlled phase separation between the organic and inorganic phase
We fabricate our films by spin-coating precursor solutions comprising lead bromide (PbBr2), cesium bromide (CsBr), and PEABr in dimethyl sulfoxide (DMSO)
Summary
This suggests that perovskite crystal growth is impeded in the presence of PEABr. The crystallite size is reduced further with increasing the PEABr ratio up to 40%, as shown in. AFM images decreases from approximately 20 nm (0% PEABr) to approximately 1.7 nm (40% PEABr) This result is consistent with previous reports of MAPbBr3 films, for which BABr addition can dramatically enhance the film uniformity[6]. A preferential orientation of crystallites with respect to the substrate is induced by adding PEABr4,15 Both synchrotron 2D grazing incidence XRD (GIXRD)
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