Candidate: Saad Mobarak
Date: November 27, 2025
Time: 3:00pm
Location: EIT 3145
Supervisor: Dr. Hany Aziz
All are welcome!
Abstract:
Colloidal quantum dot light-emitting devices (QLEDs) have attracted significant interest for next-generation emissive display and lighting applications owing to their narrowband emission, tunable bandgaps, and compatibility with solution-based fabrication. Their emissive layers (EMLs), composed of colloidal quantum dots (QDs), exhibit discrete energy states and size-dependent bandgaps, allowing precise spectral tunability and narrow emission linewidths (FWHM < 25 nm). The high photoluminescence quantum yield (PLQY), excellent photochemical stability, and compatibility with low-temperature fabrication processes make them highly suitable for large-area and flexible devices. Collectively, these properties position QLEDs as strong contenders to replace organic-LEDs (OLEDs) in future display technologies, offering improved color saturation, reduced power consumption, and enhanced manufacturing versatility.
Despite these advantages, QLEDs still face fundamental challenges related to charge transport and device efficiency. In particular, the use of organic electron transport layers (ETLs) has been limited due to their perceived low electron mobility and inferior performance compared to inorganic metal-oxide ETLs. However, organic ETLs remain attractive for certain device architectures because of their solution processability, tunable energy levels, and compatibility with low-temperature and flexible fabrication. Moreover, organic layers can form smoother, defect-free interfaces with the QD EMLs compared to metal-oxide ETLs, which may introduce interfacial traps or cause damage during deposition. While the low efficiency of QLEDs employing organic ETLs has conventionally been attributed to their poor electron mobility, the findings presented in this thesis reveal that uncontrolled electron leakage from the QD EML to the hole transport layer (HTL) plays a more dominant role. Based on the finding, the design and optimization of multilayer organic ETL architectures with electron-blocking interfaces effectively suppress electron leakage, leading to improved charge balance and enhanced device efficiency. Using this approach, both red and green QLEDs achieve maximum EQEs approaching 10%, representing among the highest reported values for devices employing organic ETLs.
Another limitation in QLEDs is their limited amenability to high-resolution patterning of RGB arrays for full-color displays. Conventional techniques, such as inkjet printing or photolithography, often suffer from limited resolution, QD degradation, or complex processing steps that can compromise device performance. This thesis also presents a novel RGB patterning technique based on metal-induced quenching. Thin metal layers are selectively deposited via a shadow mask onto target areas of the QD EMLs, where subsequent metal diffusion into the EML locally suppresses luminescence through non-radiative energy transfer, while unexposed regions retain their intrinsic emission characteristics. Optical and morphological characterization shows that metal-coated QD regions develop increased surface roughness and island-like features, indicating that metal diffusion into the QD layer plays a significant role in facilitating non-radiative quenching. Using this approach, we demonstrate the fabrication of devices containing multiple QLEDs from a single multilayer stack, each producing spectrally pure electroluminescence (EL) without detectable parasitic emission. Additional patterned structure demonstrates controlled microscale emission at the device level, establishing the feasibility of achieving spatial color definition with high precision. These results validate metal-induced quenching as an effective methodology for QLED color patterning and provide insight into metal-QD interactions.