Revealing Interactions between Hole-Transporting Layers and Perovskite Quantum Dots for Electroluminescence

Perovskite quantum dots (PeQDs) are promising nanoscale emitters in a generation of high-performance, large-area, and low-cost light-emitting diodes (LEDs) due to their superior emissive properties and excellent solution processability. Despite the tremendous advancement in luminescence efficiency in PeQDs, the design principle of the hole-transporting layer for PeQDs-based LEDs is still limited. Here, we investigate the discrepancy in electroluminescence properties of PeQDs-based LEDs with two widely used hole-transporting layers, namely, poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine] (PTAA) and poly(9,9-dioctylfluorene-co-N-(4-(3-methylpropyl)) diphenylamine) (TFB). The results show that the TFB-based PeQD-LEDs exhibit much inferior performance than the PTAA-based device (7% vs 18% for external quantum efficiency) although the PeQDs show better optical properties when depositing on TFB hole-transporting layers. Theoretical calculation and comprehensive spectroscopic analysis indicate a weaker interaction between PeQDs and TFB polymers, which is attributed to the larger steric hindrance of TFB than that of PTAA. As a result, electrical characterizations identify a poor hole injection efficiency from the TFB to the PeQDs emissive layer when compared with the PTAA hole-transporting layers, thus leading to poor device performance. This work reveals the interaction between the hole-transporting layer and PeQDs on the performance of electroluminescence beyond the energy level and mobility of hole-transporting materials, which promotes an understanding of the hole injection mechanism in PeQDs-based LEDs.