Zhao, Yining; (2025) Synthesis and Applications of Fully Inorganic Halide Perovskite Quantum Dots in Optoelectronics. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

Optoelectronic devices, which convert light signals into electrical signals, are integral to modern life, with applications spanning optical sensors, photodetectors, energy storage, and imaging systems. Despite the wide variety of photosensitive materials available for these devices, challenges related to fabrication processes, material properties, and manufacturing costs have hindered their advancement. Non-vacuum processed optoelectronics represent a significant advancement in the field, offering cost-effective and scalable alternatives to traditional vacuum-based fabrication techniques. In recent years, metal halide perovskites have emerged as promising candidates for high-performance optoelectronic devices. These materials offer advantages such as low-temperature solution processing, cost-effective fabrication, high defect tolerance, and tunable emission wavelengths. However, their practical implementation remains constrained by inherent issues such as environmental instability and self-absorption. This thesis focuses on optimizing all-inorganic perovskite quantum dots (PQDs) to address these challenges and exploring their application in three key optoelectronic devices: solar cells, photodetectors, and scintillators. In the solar cell study, cesium lead bromide (CsPbBr3) PQDs were synthesized via a one-pot method and utilized as the light-absorbing layer. Optimizing the PbBr2 precursor ratio improved the crystal structure and thin-film morphology, enhancing optical properties. Additionally, manganese (Mn) doping was shown to improve the environmental stability of CsPbBr3 PQDs, facilitating subsequent anion exchange. Iodine exchange extended the light absorption range, but challenges in film deposition limited the solar cell’s power conversion efficiency to 2.58%, highlighting the need for further optimization. In the photodetector research, CsPbBr3 PQDs were integrated into a paper-based photodetector in combination with single-layer graphene (SLG). The PQDs were printed onto a paper substrate using a microplotting technique with micrometer resolutions, enhancing the photoconductive gain mechanism. This device achieved an exceptional external responsivity of approximately 82,000 AW-1 at 520 nm under low operating voltage, surpassing the performance of state-of-the-art paper-based photodetectors and demonstrating significant potential for flexible electronics. In the scintillator study, modified CsPbBr3 PQDs were synthesized for scintillator applications. The introduction of long-chain oleylamine (OAm) during synthesis resulted in PQDs with high crystallinity, excellent stability, and enhanced optical properties. To mitigate reabsorption losses, Rhodamine 6G (r6G) was incorporated into the PQDs, creating a hybrid material capable of reabsorption-free scintillation and stable radioluminescence. This hybrid material demonstrated strong potential for real-time dynamic X-ray imaging applications. This work highlights the versatility of PQDs and their potential in advancing optoelectronic device performance. Future efforts will focus on further material optimization and extending their applications in high-performance optoelectronic systems.

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