Recently, quantum dots (QDs) based on low-band-gap metal chalcogenides have been widely explored as photon harvesters in quantum dot solar cells due to their tunable band gap and high absorption coefficient. Colloidal quantum dot (CQD) solar cells made from lead sulfide (PbS) QDs have achieved a power efficiency of ~ 8%. These types of solar cells consist of a compact/mesoporous TiO2 layer on a transparent conducting oxide (TCO), followed by a PbS QD layer deposited, and finally a metal which serves as a back contact. In these devices, it is important to control the band gap as well the band position of the QDs to efficiently inject electrons into TiO2 and holes into the metal electrode. In this work, studies were performed to control the band gap and tune the relative band positions of ternary lead chalcogenide (PbSexS1-x) QDs through composition control and surface ligand modification. These effects were studied with UV-Vis absorption and photoelectron spectroscopies. Multilayer CQD solar cells were fabricated to investigate charge mobility between QD layers with different relative band positions. We show that band engineering can be applied to PbSexS1-x QDs in order to create a favorable band diagram and achieve enhanced photogenerated carrier collection in multilayer CQD devices.

Band engineering of ternary lead chalcogenide quantum dots for colloidal quantum dot solar cells

248th National Meeting (2014)

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