The candidate has conducted the following work through the project:
(1) Synthesized/fabricated high-quality QDs that are suitable for being used as part of the hybrid materials. The photoluminescence quantum yield (PLQY) for the materials have been improved relatively 30-50% for QDs in all band gap ranges, compared with what the group could achieve previously. This was achieved by new development in the synthesis and purification methods.
(2) Fabricated a series of OSCs/QDs hybrid materials. The candidate has identify several material combinations that can achieve ~100% TET efficiency. The overall PLQYs of the materials have also been improved progressively during the projects, due to the improved processing methods.
(3) The performance of the hybrid materials have been characterized by a series of steady-state techniques, in order to confirm the PLQYs, TET efficiency, material morphology and composition, and the relevance between these have been related, hence some key factors to the overall performance have been identified.
(4) The TET processes in the hybrid materials have been studied in details, using time-resolved spectroscopy set-ups. The processes of the generation of triplets in the OSCs, transfer to the QDs, and re-emission from the QDs have been observed in details, and now the timescale for each to occur are clear in each hybrid material.
(5) Prototype photon-multiplying films based on the hybrid materials have been fabricated. The TET efficiency between the materials can be close to 100%, and the multiplication factor can now achieve ~1.3. However, the baseline emission yield of QDs are still low, due to problems of energy level mismatch, PL quenching due to aggregations, and likely some other compatibility problems between the materials, so the overall PLQY of the system is still relatively low.
(6) The candidate has also discovered some unusually fast exciton transport behaviour in pure QD solid films at the very early timescales. This can potentially provide important guidance to both the hybrid materials and the general society that study nano-materials with excitonic features.
For future work, the main targets would be to improve the baseline PLQY of the QDs, solve the compatibility problems between the materials, and search for more OSCs that have higher energy levels to match with QDs that have higher PLQYs.
Some of the findings have been included in the group’s publications. Several manuscripts are also currently under-review or close to submission to scientific journals. The delay was mainly caused by the COVID-19 pandemic and the lockdown/lab restrictions from Mar 2020.
