Engineering surface ligands on colloidal quantum dots for solar energy harvesting

Abstract

Summary form only given, as follows. The complete presentation was not made available for publication as part of the conference proceedings. Colloidal quantum dots (CQDs) can be solution-processed and obtained in low cost and large quantity, and CQD-based devices have been reported in many applications. Here we will showcase our recent works on chalcogenide CQDs for applications in solar energy harvesting. The surfaces of highly monodispersed chalcogenide CQDs (i.e. PbS, CdSe) are covered with long-chain molecular ligands. These surface ligands stabilize CQDs in organic solvents but need to be replaced with short-chain molecules, even single atoms, in applications where fast charge transport between CQDs is required. If this ligand exchange process happens when forming CQD solids in the device, it is called solid-state ligand exchange (SSLE). We have demonstrated CQD-based flexible touch sensors [1], narrow-band photodetectors [2], ultrafast photodiodes [3] and solar cells [4] using SSLE. The long-chain ligands can also be exchanged to short ones in organic solvents, and this solution-phase ligand exchange (SPLE) method provides better charge transport and more flexibility for engineering CQDs into devices [5]. In the presentation, we will discuss two applications of SPLE-produced CQDs for solar energy harvesting - PbS CQDs for homojunction solar cells [6] and CdSeS/ZnS core-shell CQDs for luminescent solar concentrators [7].