Light-emitting diodes (LEDs) are crucial components in display technology, and the next generation requires meeting the Rec. 2020 color gamut standard. Metal-halide perovskites, with their narrowband emissions and tunable bandgap, are promising candidates. While perovskite LEDs (PeLEDs) have achieved EQEs approaching 30%, their intrinsic instability hinders widespread adoption. This research explores a hybrid approach, combining the high color purity of perovskite emitters with the mature technology of organic LEDs (OLEDs). This strategy leverages the compatibility of perovskite deposition by thermal evaporation with existing OLED production lines, offering a path towards commercialization. Tandem LEDs, connecting multiple electroluminescence units via an interconnecting layer (ICL), provide a mechanism for integrating different technologies and improving operational lifetime by reducing current at the same luminance, a particular advantage for inherently unstable PeLEDs. This work introduces a hybrid perovskite-organic LED with an efficient ICL composed of HAT-CN/MoO₃/CBP, aiming to accelerate the commercialization of perovskite-based display technology. The design focuses on achieving high transmittance and good electrical connection, with a green-emitting PeLED and OLED with similar photoluminescence peaks to minimize photon reabsorption.

The introduction thoroughly reviews the current state of perovskite and organic LED technologies, highlighting the advantages and limitations of each. It cites numerous publications demonstrating the progress in PeLED efficiency and the challenges related to their instability. The review also covers existing hybrid display technologies, such as quantum dot liquid crystal TVs and white light LEDs combining QLEDs and OLEDs, placing the current work within the context of ongoing advancements in display technology. The literature supports the rationale behind the proposed hybrid approach and the use of a tandem LED structure for enhanced performance and stability.

The study utilizes a tandem structure, vertically stacking a bottom PeLED and a top CBP:Ir(ppy)₂(acac)-based OLED. The critical component is a novel ICL consisting of HAT-CN, MoO₃, and CBP. The HAT-CN acts as an electron generation/separation layer, CBP as a hole generation/separation layer, and MoO₃ as a charge enhancement layer. The ultra-thin MoO₃ layer (approximately 1 nm) facilitates hole tunneling and enhances carrier concentration. The energy band diagram of the hybrid device is analyzed to predict carrier injection and transport. Both PeLED and OLED subunits were fabricated and characterized individually, and their performance was compared to the hybrid device. The electrical properties of the ICL were investigated using two configurations: HAT-CN/CBP (CGL) and HAT-CN/MoO₃/CBP (m-CGL). Theoretical simulations using a drift-diffusion model, coupled with the Poisson equation and field-dependent Miller-Abrahams theory, were employed to analyze charge density, electric field distribution, and recombination rates in both ICL configurations. The simulations predicted a significant enhancement in charge generation and separation with the inclusion of the MoO₃ layer. Experimental characterization included J-V and C-V measurements of ICL devices with varying MoO₃ thicknesses (0-3 nm), atomic force microscopy (AFM) and conductive AFM (c-AFM) for morphological and conductivity analysis, and XPS to investigate MoO₃ diffusion into the HAT-CN film. Surface temperature measurements were conducted at various luminance levels to assess Joule heating. Finally, the EL performance of hybrid LEDs with both CGL and m-CGL was compared, including luminance, EQE, CIE coordinates, and operational lifetime.

The key findings demonstrate the superior performance of the hybrid LED with the m-CGL compared to the device with the CGL. The m-CGL hybrid LED exhibited a significantly narrower full-width-at-half-maximum (FWHM) of 31 nm compared to 42 nm for the CGL device, indicating enhanced color purity. The m-CGL LED achieved a peak EQE of 43.42%, a maximum luminance of 176,166 cd m⁻², and a long half-lifetime of 42,080 h at 100 cd m⁻². The simulations showed a substantial increase in charge density and electric field with the m-CGL, confirming its role in efficient carrier generation and separation. J-V and C-V measurements of the ICLs further supported the enhanced charge generation and transport capability of the m-CGL. The lower surface temperature observed in the m-CGL device at high luminance levels underscores the effectiveness of MoO₃ in suppressing Joule heating. The statistical analysis of the maximum EQE values demonstrated good device-to-device reproducibility. The operational stability tests, conducted under different conditions and with different perovskite systems, validated the improvements in the hybrid LED's lifetime.

The results clearly demonstrate the effectiveness of the hybrid perovskite-organic LED architecture and the crucial role of the m-CGL in achieving high efficiency and stability. The significant improvement in EQE, luminance, and operational lifetime compared to both individual components and the CGL device showcases the synergistic effect of integrating perovskite and organic materials. The enhanced charge generation, separation, and transport facilitated by the MoO₃ layer in the m-CGL effectively address the limitations of perovskite instability and Joule heating, crucial factors for long-term operation. The narrow linewidth confirms the maintenance of perovskite's high color purity in the hybrid device. The findings contribute significantly to the development of next-generation display technologies, paving the way for highly efficient, stable, and color-pure LEDs.

This research successfully fabricated and characterized high-performance hybrid perovskite-organic LEDs with an EQE exceeding 40% and a remarkably long operational lifetime. The optimized interconnecting layer with MoO₃ significantly improved charge generation, transport, and reduced Joule heating. This work provides a promising approach to overcome the stability limitations of perovskite LEDs, offering a pathway toward practical applications in high-definition displays. Future research could explore different perovskite compositions, optimize the ICL further, and investigate encapsulation strategies to enhance long-term stability in real-world conditions.

The study primarily focuses on green-emitting LEDs. Further research is needed to explore the applicability of this hybrid approach to other color ranges. While the study demonstrates significant improvements in operational lifetime, long-term stability tests under diverse environmental conditions are needed to fully assess the device's robustness. The simulations, while insightful, are based on certain model assumptions; further experimental validation might be necessary to refine the understanding of the underlying physical processes.