Realization of Highly Efficient InP Quantum Dot Light-Emitting Diodes through In-Depth Investigation of Exciton-Harvesting Layers

Quantum dot light-emitting diodes (QLEDs) are considered promising candidates for several optoelectronic applications; however, they are plagued by the over-injection of electrons compared to holes, which limits device efficiency. Studies have attempted to reuse the leaked electrons and transfer recombination energies via inserting an exciton-harvesting layer (EHL) between the emissive layer (EML) and hole transport layer (HTL). This study conducts a detailed analysis of the energy transfer mechanisms to obtain better insights into improving the device performance. First, by analyzing the electroluminescence (EL) spectra and exciton dynamics, the effect of EHLs comprising phosphorescence (PH) or thermally activated delayed fluorescence (TADF) blue dopant is compared. Through parallel incorporation of those EHLs on QLEDs and organic LEDs, the minimal contribution of the PH-EHL to energy transfer in QLEDs is confirmed, whereas the TADF-EHL has a significant contribution. Second, highly efficient top-emission green QLEDs with the TADF-EHL are achieved. They exhibit a maximum luminance (L) and current efficiency (CE) of 40700 cd m⁻² and 68.0 cd A⁻¹, respectively, which are the highest among the reported values for green-emitting InP QLEDs. The proposed approaches are expected to provide aid in the realization of highly efficient QLEDs from the analysis to the device optimization stage.