In the last decade, nanoscience has emerged as a novel technology due to its versatility to be employed in many research areas. Nanoscience studies the structures and materials on the nanometers scale. One of the most promising nanomaterials, colloidal quantum dots have been deeply studied in the last decades for their extraordinary optoelectronic properties and their versatility in order to use in different fields, such as bioimaging, sensor, optoelectronic devices, etc.
Colloidal quantum dots technologies have burst in both academic and industrial field. Quantum dots are defined as nanometer scale semiconductor crystal with a physical size smaller than exciton Bohr radius, and as consequence quantum confinement. This means that their bandgap changes according to their size. Regarding the optical properties, they show broad absorption, narrow emission and color purity, especially when compared to organic semiconductors.
The present thesis is focused on the synthesis of different quantum dots as well as their use in LEDs, perovskites solar cells and sensors. Three different Quantum Dots have been synthetized: cadmium, perovskites and carbon based quantum dots. The first two material present a high quantum yield and narrow emission band. However their high toxicity is an important weakness. In order to avoid the use of those material we synthetized carbon quantum dots. Their low toxicity and biocompatibility is a good alternative to heavy metal-containing nanomaterials. In addition, carbon based material can be prepared using ordinary products as sugar or orange juice and solved in non-chloro solvents such as ethanol or water.
Quantum dots LEDs (QLEDs) have emerged in the last year as new LEDs generation due to better color definition over the entire visible spectrum. Basically, the structure consists of a sandwiched layer of emissive quantum dots between electron and hole transport layers, so when a bias is applied hole and electrons are radiatively recombined in the quantum dot layer emitting light.
The second application we worked on during this thesis was perovskites solar cells. Converting solar energy efficiently into either electrical or fuel sources remains one of mankind’s biggest challenges. Despite the rapid progress that has been made in recent years in research into third generation solar cells, silicon is still the biggest and most important player in the PV industry. Such new technologies, as mixed halide perovskite solar cells are quickly catching-up efficiency (the current record of efficiency is above 22% at 1 sun). The synthetized and tested CQDs as hole transport material in order to replace the actual on, Spiro-OMeTAD because of the high production cost.
Finally, a different application of QDs has been explored, two different biosensors have fabricated in order to detect and quantify elastase in human samples. We fabricated two different sensors: an Optical and an electrochemical sensors. Both sensors present better properties such as low cost, real-time and high sensitivity and specificity comparing with the conventional analytical techniques.
The work discussed in this thesis was carried out at Institute of Chemical Research of Catalonia (ICIQ) and Eurecat, the technological center of Catalonia, between March 2015 and March 2019.