Boosting Efficiency of Perovskite Light-emitting Diodes Through Compositional Engineering

The Ruddlesden-Popper (RP) perovskites are recognized as the most promising candidate for industrialized optoelectronic applications, due to their higher stability and lower defect density compared with the three-dimensional counterparts. Doping with various ions constitutes a strategic approach to tailor the characteristics of perovskite materials. Alkali and alkaline earth metal ions, with their unique sizes and charges, possess the capability to modify the lattice parameters, bandgap, and defect states of perovskites, thereby resulting in enhanced material performance. This thesis primarily focuses on investigating the impact of different alkali metal ions, specifically cesium (Cs) and potassium (K), on the optoelectronic properties of RP perovskite.

The initial investigation confirmed that the appropriate incorporation of cesium ions (Cs⁺) can partially replace the formamidinium (FA⁺) ions in the n = 3 RP perovskite, PEA₂(FAPbBr₃)₂PbBr₄. This substitution improves the lattice stability and alters the phase distribution, thereby enhancing the performance of PeLED devices.

Subsequently, we extended this to explore the effects of smaller alkali metal ions, specifically potassium ions (K⁺), and determine whether they exhibit similarities or differences compared to Cs⁺. We discovered that the addition of potassium ions can passivate defects in the perovskite, leading to an improvement in the surface morphology of the thin films and an increase in the external quantum efficiency (EQE) of PeLEDs to 7.7%.

Given the intrinsic limitations of the baseline device efficiency, we opted to modify the RP perovskite structure from n = 3 to n = 5, resulting in a significant enhancement of the baseline device efficiency to 13.60%. At this stage, doping with KBr can alter the local electric field distribution of the perovskite material, shield charged defects, and suppress carrier trapping. This synergistic strategy of dielectric shielding and defect passivation leads to a remarkable increase in the photoluminescence quantum yield (PLQY) of the perovskite thin films from 66% to 95% and elevates the EQE to approximately 21%.

In conclusion, the comprehensive investigation into the utilization of alkali metal ions in quasi-two-dimensional RP perovskites provides an inspiring foundation for enhancing the performance of optoelectronic devices in future developments.

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