title: Real-Space Mapping of Surface Trap States in CIGSe Nanocrystals Using 4D Electron Microscopy.
abstract: Surface trap states in copper indium gallium selenide semiconductor nanocrystals (NCs), which serve as undesirable channels for nonradiative carrier recombination, remain a great challenge impeding the development of solar and optoelectronics devices based on these NCs. In order to design efficient passivation techniques to minimize these trap states, a precise knowledge about the charge carrier dynamics on the NCs surface is essential. However, selective mapping of surface traps requires capabilities beyond the reach of conventional laser spectroscopy and static electron microscopy; it can only be accessed by using a one-of-a-kind, second-generation four-dimensional scanning ultrafast electron microscope (4D S-UEM) with subpicosecond temporal and nanometer spatial resolutions. Here, we precisely map the collective surface charge carrier dynamics of copper indium gallium selenide NCs as a function of the surface trap states before and after surface passivation in real space and time using S-UEM. The time-resolved snapshots clearly demonstrate that the density of the trap states is significantly reduced after zinc sulfide (ZnS) shelling. Furthermore, the removal of trap states and elongation of carrier lifetime are confirmed by the increased photocurrent of the self-biased photodetector fabricated using the shelled NCs.
authors.affiliation: Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Riya
authors.initials: R
authors.lastname: Bose
authors.affiliation: Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Ashok
authors.initials: A
authors.lastname: Bera
authors.affiliation: Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Manas R
authors.initials: MR
authors.lastname: Parida
authors.affiliation: Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Aniruddha
authors.initials: A
authors.lastname: Adhikari
authors.affiliation: Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Basamat S
authors.initials: BS
authors.lastname: Shaheen
authors.affiliation: Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Erkki
authors.initials: E
authors.lastname: Alarousu
authors.affiliation: Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Jingya
authors.initials: J
authors.lastname: Sun
authors.affiliation: Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Tom
authors.initials: T
authors.lastname: Wu
authors.affiliation: Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Osman M
authors.initials: OM
authors.lastname: Bakr
authors.affiliation: Solar and Photovoltaics Engineering Research Center, Physical Sciences and Engineering Division, King Abdullah University of Science and Technology (KAUST) , Thuwal 23955-6900, Kingdom of Saudi Arabia.
authors.forename: Omar F
authors.initials: OF
authors.lastname: Mohammed
keywords: 4D scanning ultrafast electron microscopy; CIGSe; charge carrier dynamics; semiconductor nanocrystals; shelling; surface traps