Quasi-type II CuInS2/CdS core/shell quantum dots

Kaifeng Wu; Guijie Liang; Degui Kong; Jinquan Chen; Zheyuan Chen; Xinhe Shan; James R McBride; Tianquan Lian

doi:10.1039/c5sc03715h

Quasi-type II CuInS₂/CdS core/shell quantum dots

Chem Sci. 2016 Feb 1;7(2):1238-1244. doi: 10.1039/c5sc03715h. Epub 2015 Nov 12.

Authors

Kaifeng Wu¹, Guijie Liang², Degui Kong³, Jinquan Chen¹, Zheyuan Chen¹, Xinhe Shan¹, James R McBride⁴, Tianquan Lian¹

Affiliations

¹ Department of Chemistry , Emory University , 1515 Dickey Drive, NE , Atlanta , Georgia 30322 , USA . Email: tlian@emory.edu.
² Hubei Key Laboratory of Low Dimensional Optoelectronic Materials and Devices , Hubei University of Arts and Science , Xiangyang 441053 , Hubei Province , P. R. China.
³ College of Electronic Engineering , Heilongjiang University , Harbin 150080 , P. R. China.
⁴ Department of Chemistry , The Vanderbilt Institute of Nanoscale Science and Engineering , Vanderbilt University , Nashville TN 37235 , USA.

Abstract

Ternary chalcopyrite CuInS₂ quantum dots (QDs) have been extensively studied in recent years as an alternative to conventional QDs for solar energy conversion applications. However, compared with the well-established photophysics in prototypical CdSe QDs, much less is known about the excited properties of CuInS₂ QDs. In this work, using ultrafast spectroscopy, we showed that both conduction band (CB) edge electrons and copper vacancy (V_Cu) localized holes were susceptible to surface trappings in CuInS₂ QDs. These trap states could be effectively passivated by forming quasi-type II CuInS₂/CdS core/shell QDs, leading to a single-exciton (with electrons delocalized among CuInS₂/CdS CB and holes localized in V_Cu) half lifetime of as long as 450 ns. Because of reduced electron-hole overlap in quasi-type II QDs, Auger recombination of multiple excitons was also suppressed and the bi-exciton lifetime was prolonged to 42 ps in CuInS₂/CdS QDs from 10 ps in CuInS₂ QDs. These demonstrated advantages, including passivated trap states, long single and multiple exciton lifetimes, suggest that quasi-type II CuInS₂/CdS QDs are promising materials for photovoltaic and photocatalytic applications.