Colloidal semiconductor nanocrystals, also termed quantum dots (QDs), have been discovered around 40 years ago, which has given rise to the 2023 Nobel prize in Chemistry. They have attracted considerable interest due to their unique size-dependent optical and electronic properties. In particular, their band gap can be simply changed by adjusting their size via the so-called quantum confinement effect. It occurs for many semiconductors when at least one of their dimensions is reduced to a few nanometers. Most research has been conducted on binary cadmium- and lead-based QDs (CdSe, PbS, etc.), which cover the visible and near infrared spectral range and can be easily synthesized. However, due to the toxicity of these compounds, their use in real-life applications is strongly limited. Our team is focusing on the development of toxic heavy metal-free and environmentally benign QDs such as III-V semiconductor materials (InP, InSb), which have a high potential for use in biomedical applications, energy conversion, photocatalysis, and optoelectronics.
In this project, we want to develop synthesis methods for size- and shape-controlled III-V QDs, first in batch and then in continuous flow. Continuous flow synthesis has many advantages compared to conventional batch synthesis due to the enhanced mass and heat transfer in small-sized tubular reactors and the higher reproducibility in fully automated processes. The surface chemistry of the obtained QDs is a key parameter, which governs their chemical stability and processibility, photoluminescence quantum yield (PLQY), photostability, and electrical transport properties. Therefore, appropriate surface functionalization is required for essentially all types of applications of QDs encompassing photocatalysis, photodetectors, LEDs, and biological imaging/detection. Here, we will develop methods for the precisely controlled growth of various types of inorganic shells to passivate and stabilize the QDs, focusing on metal chalcogenides (ZnS, ZnSe) and ceramic-type materials (e.g., Al2O3, TiO2, and ZrO2) as well as combinations thereof. Characterization of the optical and structural properties will be performed using UV-vis and photoluminescence (PL) spectroscopy, time-resolved PL and PLQY measurements, Raman spectroscopy, NMR and FTIR spectroscopy, X-ray diffraction, elemental analysis, and electron microscopy.
In the second part of the project, the potential of the obtained QDs for use in NIR photodiodes as well as for the photocatalytic CO2 reduction will be evaluated.