Using High Throughput Experimentation and Atomistic Simulations to Investigate Colloidal Quantum Dots

It is widely understood that the transition to low-carbon, green energy sources is vital for combatting climate change and ensuring continued energy security. AgInS2 and CuInSe2 are ternary I-III-VI2 semiconductors which have attracted immense interest due to their large absorption in the visible light region of the electromagnetic spectrum, non-toxic components and relatively large Bohr radii. These features are attractive for use in photovoltaic applications, in particular in the formation of quantum dot sensitised solar cells (QDSSCs). Unfortunately, in comparison to their lead-based competitors they are currently less efficient however the sensitivity of their physical characteristics to changes in composition and ligand capping layer suggests broad scope for optimisation towards specific applications.
This project aimed to use high throughput flow synthesis and computer simulations to understand how to improve CuInSe2 performance in QDSSCs. However, there were significant set-backs in terms of developing a reproducible synthesis due to its sensitivity to oxygen and inconsistent Se reduction. It was therefore decided to switch focus to AgInS2 which was more easily adapted. While a repeatable flow synthesis was developed, it was noted that dual spectroscopic emissions were identified which may be due to the presence of trap-states within the band gap. Computer simulations backed up this suggestion due to the large density of states present at the Fermi level in the slab models. Adding two S bridging adatoms successfully removed this density and obtained a band gap of 0.179 eV without requiring a correction factor. While an
underestimation of the band gap, the loss of electron density and reduction in the final total energy demonstrates the ability of defects to stabilise the nanoparticle.