Real-space Mapping of Surface Trap States in CIGSe Nanocrystals using 4D Electron Microscopy

Riya Bose, Ashok Bera, Manas R. Parida, Aniruddha Adhikari, Basamat S. Shaheen, Erkki Alarousu, Jingya Sun, Tao Wu, Osman Bakr, Omar F. Mohammed

Research output: Contribution to journalArticlepeer-review

22 Scopus citations


Surface trap states in semiconductor copper indium gallium selenide nanocrystals (NCs) which serve as undesirable channels for non-radiative 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 sub-picosecond temporal and nanometer spatial resolutions. Here, we precisely map the surface charge carrier dynamics of copper indium gallium selenide NCs 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, 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.
Original languageEnglish (US)
Pages (from-to)4417-4423
Number of pages7
JournalNano Letters
Issue number7
StatePublished - May 31 2016


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