Enhancing Stability in Quantum-Dot and Perovskite Optoelectronic Devices through Compositional Engineering and Surface Treatment

Solution-processed quantum dots (QDs) and metal-halide perovskites are of interest inoptoelectronics because of their sharp color, high absorption, and bright emission. However, their further progress is hampered today by limited operating stability. In this thesis, I study how compositional engineering and surface treatment can address these stability challenges to increase durability at high efficiency. My investigation begins with stable, environment-friendly blue emitters for full-color displays. Vacancy-ordered double perovskites are lead-free, yet most are weakly emissive. I find that compositional engineering of a specific member, Rb2HfCl6, through Bi3+ doping and Cs+ alloying, transforms the non-emissive host into a moisture-resistant emitter at 466 nm with a 66% photoluminescence quantum yield. As material dimensions shrink to the QD scale, surfaces dominate, and the work then turns from engineering the bulk to focusing on the surface of QDs. A dual-ligand exchange assembles perovskite QDs into a densely-packed, ordered solid, which enhances conductivity and enables LEDs that generate 1000 cd m-2 at a voltage of 2.8 V. The reduced operating field extends the operating device stability 100-fold. With the emissive layer optimized, I then focus on charge transport layers. I address ETL instabilities from two complementary angles. First, I replace the conventional ZnMgO ETL with a bifunctional organic molecule that passivates QD surface traps and suppresses ion migration, thereby producing InP QD-LEDs with higher efficiency and improved stability. Secondly, I stabilize the ZnMgO with an ultrathin Al2O3 coating, which extended the operating lifetime tenfold. To achieve optimal device performance with balanced charge injection, I engineer the HTL via Li doping and oxygen treatment to tune the composition of the NiOₓ. The hole conductivity is improved, leading to balanced charge injection more efficient devices. Finally, I study how interfacial engineering can be applied to photovoltaics to address a large voltage loss due to interfacial traps and unfavorable band alignment in ultrawide-bandgap perovskite solar cells, a sublayer relevant to triple-junction solar cells. I find that a bifunctional molecule, positioned at a buried interface, simultaneously passivates traps and improves energy alignment, reclaiming ~30 mV of open-circuit voltage and providing a pathway to more efficient multi-junction solar cells.

Department dc:contributor.department

Electrical and Computer Engineering

Year dc:date.issued

2025

Author dc:creator

• Wan, Haoyue

Advisor dc:contributor.advisor

• Sargent, Edward

• Light emitting devices
• Optoelectronics
• Perovskite
• Quantum dots
• Solar cells

Statement dc:rights

• Attribution-NonCommercial-NoDerivatives 4.0 International

Licence dc:rights.uri

• http://creativecommons.org/licenses/by-nc-nd/4.0/

Handle dc:identifier.uri

https://hdl.handle.net/1807/150628

OAI identifier oai:identifier

oai:utoronto.scholaris.ca:1807/150628