Investigating the structure-function relationship in triple cation perovskite nanocrystals for light-emitting diode applications

Organic metal halide perovskite nanocrystals are promising candidates for light-emitting diodes due to their narrow emission bandwidth, high photoluminescence quantum yield (PLQY), and color tunability. Nevertheless, these systems suffer from thermal instability, phase impurities, and a sensitivity to processing techniques. This study reports the first synthesis of novel Cs-containing triple cation perovskite nanocrystals with nominal stoichiometry Cs_x(MA_0.17FA_0.83)_1−xPbBr₃(x= 0-0.15). The effect of Cs⁺cation incorporation is thoroughly investigated using diffraction, microscopy and solid state MAS NMR techniques. The solid state¹³³Cs MAS NMR results reveals the distribution of the Cs⁺cations is highly concentration and particle size dependent, with maximized surface/subsurface Cs⁺concentrations being achieved with the smaller 5 mol% Cs system. These characteristics directly correlate improved surface passivation and environmental stability of the triple cation system. These triple cation nanocrystals exhibit a maximum photoluminescence quantum yield of ∼93% which upon translation to nanocrystalline LED devices delivers a maximum EQE of 7.4% (30 cd A⁻¹) corresponding to a power efficiency of 34.87 lm W⁻¹. This performance represents a marked improvement compared to CsPbBr₃nanocrystals (PL quantum yield ∼50%; maximum EQE of 2.5% (7.2 cd A⁻¹)) fabricated under similar conditions.