Sunday, March 6, 2016

Abstract-Ultrafast Dynamics of Hole Injection and Recombination in Organo Metal Halide Perovskite Using Nickel Oxide as p-Type Contact Elec-Trode

The Journal of Physical Chemistry Letters

J. Phys. Chem. Lett., Just Accepted Manuscript
DOI: 10.1021/acs.jpclett.6b00238
Publication Date (Web): March 4, 2016
Copyright © 2016 American Chemical Society

There is a mounting effort to use nickel oxide (NiO) as p-type selective electrode for organo-metal halide perovskite based solar cells. Recently, an overall power conversion efficiency using this hole acceptor has reached 18%. However, ultrafast spectroscopic investigations on the mechanism of charge injection as well as recombination dynamics have yet to be studied and understood. Using time-resolved terahertz spectroscopy, we show that hole transfer is complete on the sub-picosecond time scale, driven by the favorable band alignment between the valence bands of perovskite and NiO nanoparticles (NiO(np)). Recombination between holes injected into NiO(np) and mobile electrons in the perovskite material is shown to be hundreds of ps to few ns. Due to the low conduc-tivity of NiO(np), holes are pinned at the interface and it is electrons that determines the recombination rate. This recom-bination competes with charge collection and therefore must be minimized. Doping NiO that promotes higher mobility of holes is desirable in order to prevent back recombination.

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