High Color Conversion Efficiency Realized in Graphene-Connected Nanorod Micro-Light-Emitting Diodes with Hybrid Ag Nanoparticles and Quantum Dots Using Non-Radiative Energy Transfer and Localized Surface Plasmons

As a medium for color conversion, quantum dots (QDs) can be employed in the display of full-color GaN-based Micro-Light-Emitting Diodes (µLEDs) arrays. Typically, in a system where QDs are excited by UV/blue µLEDs, QDs are coated onto the LED surface. However, due to inherent defects in QDs and significant energy loss associated with this method, the color conversion efficiency (CCE) is suboptimal. In this paper, we introduce an innovative approach where we etch a uniform nanorod (NR) array onto the surface of µLEDs. We then mix Ag nanoparticles (NPs) with QDs to fill the gaps between the nanorods. Simultaneously, we utilize the excellent conductivity, transparency, and high strength of graphene to create a transparent conductive electrode on the nanopillar surface. This electrode serves to connect individual nanorods and enhance current spreading. The nanorod array's structure significantly reduces the distance between the QDs and the quantum well (QW), reducing energy loss from the excitation light source through a non-radiative energy transfer (NRET) mechanism. Additionally, the Ag NPs function as local surface plasmons (LSPs) in luminescent systems, further enhancing the CCE of QDs via the NRET mechanism. In this study, we compare the effects of two types of Ag NPs with different absorption resonance peaks on device performance. Our results demonstrate that Ag NPs with absorption resonance peaks matching the emission wavelength of QDs play a more crucial role in the composite system. This configuration achieves a CCE of 77.78% for µLEDs with nanorod arrays, operating at a current of 10 mA. Compared to the conventional planar µLED structure with QDs spin-coated on the surface, our proposed method improves the CCE of µLEDs by an impressive 285%. This outcome underscores the significant contribution of the NR structure and LSPs in enhancing the CCE of QD- µLEDs.