Abstract-Time-resolved terahertz spectroscopy reveals the influence of charged sensitizing quantum dots on the electron dynamics in ZnO

Sesha Bamini N.,^ab   Hynek Němec,^c   Karel Žídek,^a  Mohamed Abdellah,^ad   Mohammed J. Al-Marri,^e  Pavel Chábera,^a   Carlito Ponseca,^a   Kaibo Zheng*^ae and  Tönu Pullerits*^a  

http://pubs.rsc.org/en/content/articlelanding/2017/cp/c6cp07509f#!divAbstract

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Corresponding authors

^a

Department of Chemical Physics and NanoLund, Lund University, Box 124, 22100 Lund, Sweden
 E-mail: kaibo.zheng@chemphys.lu.se,tonu.pullerits@chemphys.lu.se

^b

National Center for Ultrafast Processes, University of Madras, Chennai 600113, India

^c

Institute of Physics, Czech Academy of Sciences, Na Slovance 2, 18221 Prague, Czech Republic

^d

Department of Chemistry, Faculty of Science, South Valley University, Qena 83523, Egypt

^e

Gas Processing Center, College of Engineering, Qatar University, P.O. Box 2713, Doha, Qatar

Photoinitiated charge carrier dynamics in ZnO nanoparticles sensitized by CdSe quantum dots is studied using transient absorption spectroscopy and time-resolved terahertz spectroscopy. The evolution of the transient spectra shows that electron injection occurs in a two-step process, where the formation of a charge transfer state (occurring in several picoseconds) is followed by its dissociation within tens of picoseconds. The photoconductivity of electrons injected into the ZnO nanoparticles is lower than that of charges photogenerated directly in ZnO. We conclude that the motion of injected electrons in ZnO nanoparticles is strongly influenced by their interaction with positive charges left in the sensitizing quantum dots.