DEVELOPMENT OF ZINC CHALCOGENIDE BASED SHELL LAYERS FOR COLLOIDAL QUANTUM WELLS

Date

2025-1-06

Author

Aldemir, Çağatay Han

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Colloidal nanoplatelets (NPLs) possess unique optical properties and electronic structures, including narrow emission bandwidths, suppressed Auger recombination, and directional emission, which make them ideal candidates for light-emitting devices (LEDs). Among the various types of NPLs explored for LED applications, cadmium-containing core/shell structures are the most extensively studied in the literature. However, cadmium-based shells face two significant challenges. First, they are toxic, raising health and environmental concerns. Second, they exhibit quasi-type II band alignment, causing the electron wavefunction to delocalize across the entire NPL volume. This delocalization reduces the recombination probability and, consequently, the overall efficiency of the LEDs. To address these issues, we propose developing zinc chalcogenide-based shell layers for colloidal NPLs, offering critical advantages over cadmium-based counterparts. Initially, we synthesized CdSe/ZnSe core/shell NPLs that emit in the 615–630 nm range, achieving an average photoluminescence quantum yield (PLQY) of 40–50%. Furthermore, we identified an important relationship between the lateral dimensions of the CdSe core NPLs and the emission linewidths of the core/shell structures: smaller lateral dimensions of the core result in narrower emission linewidths of the core/shell NPLs. To enhance the PLQY further, we deposited an additional ZnS shell layer onto the CdSe/ZnSe core/shell NPLs. This resulted in CdSe/ZnSe/ZnS core/multi shell heterostructures with a significantly improved PLQY of 80–90%. Using these highly efficient NPLs, we successfully fabricated solution-processed NPL-based LEDs. These LEDs demonstrated an external quantum efficiency (EQE) of 3.82% and a maximum brightness of 6477 cd/m². Our findings demonstrate the potential of zinc chalcogenide-based shell layers to replace cadmium-based counterparts in optoelectronic applications, paving the way for safer and more efficient light-emitting technologies.

Subject Keywords

colloidal semiconductor nanocrystals, colloidal nanoplatelets, colloidal quantum wells, core shell heterostructures, light-emitting devices

URI

https://hdl.handle.net/11511/113837

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Graduate School of Natural and Applied Sciences, Thesis