Coulomb Shifts upon Exciton Addition to Photoexcited PbS Colloidal Quantum Dots

Abstract

Using ultrafast hyperspectral transient absorption (TA) spectroscopy, we determine the biexciton addition energies in PbS quantum dots (QDs) with different sizes when either a cold or a hot electron–hole pair is added to a QD already containing a cooled exciton. The observed dependence of this so-called biexciton addition energy on the QD diameter and the exciton energy can be rationalized by interpreting the addition energies as the result of an imbalance in the Coulomb interactions between the newly created carriers and the carriers already present in a QD. The obtained results are therefore relevant from both a fundamental and practical point of view. They provide experimental data on Coulomb interaction between charge carriers in confined semiconductors that can be compared with theoretical estimates. Moreover, understanding the way hot–cold biexciton addition energies influence the transient absorption spectrum adds a new element to the transient absorption toolbox for the optoelectronic properties o...