Rubidium as an Alternative Cation for Efficient Perovskite Light-Emitting Diodes

Abstract

Incorporation of rubidium (Rb) into mixed lead halide perovskites has recently achieved record power conversion efficiency and excellent stability in perovskite solar cells. Inspired by these tremendous advances in photovoltaics, this study demonstrates the impact of Rb incorporation into MAPbBr-based light emitters. Rb partially substitutes MA (methyl ammonium), resulting in a mixed cation perovskite with the formula MARb PbBr. Pure MAPbBr crystallizes into a polycrystalline layer with highly defective sub-micrometer grains. However, the addition of a small amount of Rb forms MARb PbBr nanocrystals (10 nm) embedded in an amorphous matrix of MA/Rb Br. These nanocrystals grow into defect-free sub-micrometer-sized crystallites with further addition of Rb, resulting in a 3-fold increase in exciton lifetime when the molar ratio of MABr/RbBr is 1:1. A thin film fabricated with a 1:1 molar ratio of MABr/RbBr showed the best electroluminescent properties with a current efficiency (CE) of 9.45 cd/A and a luminance of 7694 cd/m. These values of CE and luminance are, respectively, 19 and 10 times larger than those achieved by pure MAPbBr devices (0.5 cd/A and 790 cd/m). We believe this work provides important information on the future compositional optimization of Rb-based mixed cation perovskites for obtaining high-performance light-emitting diodes.

Doping and Photon Induced Defect Healing of Hybrid Perovskite Thin Films: An Approach Towards Efficient Light Emitting Diodes

“…As prepared MAPbBr 3 and MA 0.87 Cs 0.13 PbBr 3 films consisted of clusters of NCs with average sizes of 68 and 61 nm, respectively (Figure a,b, e,f). Similar to SEM images, TEM images indicates a reduction in NC size with Cs doping ,,. Upon UV exposure, the average size of MAPbBr 3 crystallites increases to 95 nm and they form clusters.…”

“…With CsBr doping, Cs3d binding energy peak appear at 724.10 eV for Cs3d5/2 and 738.10 eV for Cs3d3/2. Additionally, N1s (the N1s peak can be assigned to (N*−C−N) + bond with MA+ cations) peak intensity decreases with Cs doping and appears at 401.72 eV, confirming partial replacement of MA by Cs ,. Upon UV irradiation, MAPbBr 3 thin films depicted similar binding energy values whereas the intensity of elements varies as shown in Figure 1d and Figure S3a‐d.…”

“…To further the verification of the effect of UV irradiation on the binding states of MABr and CsBr with PbBr 2 (DMSO)x complexes, we performed the XPS characterizations shown in Figure d,e, and Figure S3. The survey spectra of MAPbBr 3 films depict binding energy of Br3d (∼67.98 eV), Pb4f (∼137.98 and 142.86 eV, spin‐orbital splitting) and N1s (401.72 eV), confirming the formation of the cubic phase of perovskites ,. With CsBr doping, Cs3d binding energy peak appear at 724.10 eV for Cs3d5/2 and 738.10 eV for Cs3d3/2.…”

“…MAPbBr 3 perovskite solution is prepared with the same recipe as given in our previous report . For MA x Cs 1‐x PbBr 3 , a third precursor, CsBr, is added to obtain a mixed halide perovskite precursor, and MA 0.87 Cs 0.17 PbBr 3 is found to be the optimized composition.…”

“…Spreading of the SAED pattern of the as‐prepared MAPbBr 3 and MA 0.87 Cs 0.13 PbBr 3 films suggests a high defect density of NCs. The perovskite crystals appear darker than the background due to heavy elements (most likely Pb, Figure a inset) . The background consists of MABr that acts as a matrix for the crystallites (Figure 3a inset).…”