Surface and Interface Chemistry in Colloidal Quantum Dots for Solar Applications studied by X-ray Photoelectron Spectroscopy

Control of the surface and interface chemistry of colloidal quantum dots (CQDs) is critical to achieving a product with good air stability and high performing optoelectronic devices. Through various surface passivation treatments, vast
improvements have been made in fields such as CQD photovoltaics, however devices have not currently reached commercial standards. We show how a better understanding of exactly how surface treatments act on CQD surfaces, and the
effect surface composition bestows on air stability and device performance can be achieved with X-ray photoelectron spectroscopy (XPS). We illustrate this with PbS-based CQDs, using XPS to measure oxidation processes, and to quantify the
composition of the topmost surface layer after different surface treatments. We also demonstrate the use of synchrotron radiation-excited depth-profiling XPS, a powerful technique for determining the surface composition, chemistry and structure of CQDs. This review describes our recent progress in characterization of CQD surfaces using SR-excited depth profiling XPS and other photoemission techniques.