title: Trap-State Suppression and Improved Charge Transport in PbS Quantum Dot Solar Cells with Synergistic Mixed-Ligand Treatments.
abstract: The power conversion efficiency of colloidal PbS-quantum-dot (QD)-based solar cells is significantly hampered by lower-than-expected open circuit voltage (VOC). The VOCdeficit is considerably higher in QD-based solar cells compared to other types of existing solar cells due to in-gap trap-induced bulk recombination of photogenerated carriers. Here, this study reports a ligand exchange procedure based on a mixture of zinc iodide and 3-mercaptopropyonic acid to reduce the VOCdeficit without compromising the high current density. This layer-by-layer solid state ligand exchange treatment enhances the photovoltaic performance from 6.62 to 9.92% with a significant improvement in VOCfrom 0.58 to 0.66 V. This study further employs optoelectronic characterization, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy to understand the origin of VOCimprovement. The mixed-ligand treatment reduces the sub-bandgap traps and significantly reduces bulk recombination in the devices.
authors.affiliation: ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860, Castelldefels (Barcelona), Spain.
authors.forename: Santanu
authors.initials: S
authors.lastname: Pradhan
authors.affiliation: ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860, Castelldefels (Barcelona), Spain.
authors.forename: Alexandros
authors.initials: A
authors.lastname: Stavrinadis
authors.affiliation: ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860, Castelldefels (Barcelona), Spain.
authors.forename: Shuchi
authors.initials: S
authors.lastname: Gupta
authors.affiliation: ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860, Castelldefels (Barcelona), Spain.
authors.forename: Yu
authors.initials: Y
authors.lastname: Bi
authors.affiliation: ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860, Castelldefels (Barcelona), Spain.
authors.forename: Francesco
authors.initials: F
authors.lastname: Di Stasio
authors.affiliation: ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860, Castelldefels (Barcelona), Spain.|ICREA-Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010, Barcelona, Spain.
authors.forename: Gerasimos
authors.initials: G
authors.lastname: Konstantatos
keywords: VOC deficit; quantum dots; recombination; solar cells; surface passivation