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Elucidating the relationship between crystallo-chemistry and optical properties of CIGS nanocrystals

Lookup NU author(s): Dr Stevin Pramana

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This is the authors' accepted manuscript of an article that has been published in its final definitive form by Institute of Physics Publishing, 2017.

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Abstract

© 2016 IOP Publishing Ltd. The performance of solar cells fabricated using Cu(In,Ga)(S,Se)2 nanocrystal (NC) inks synthesized using the hot injection method has yielded efficiencies up to 12% recently. The efficiency of these devices is highly dependent on the chemical composition and crystallographic quality of the NCs. The former has been extensively discussed as it can be easily correlated to the optical properties of the film, but detailed crystallographic structure of these NCs has scarcely been discussed and it can influence both the optical and electrical properties. Hence both chemical composition and crystal structure should be explored for these NCs in order for this material to be further developed for application in thin film solar cells. In this work, a thorough investigation of the composition and crystal structure of CuInxGa1-xSe2 NCs synthesized using the hot injection method over the entire composition range (0 ≤x ≤1) has been conducted. Raman spectroscopy of the NCs complements the information derived from x-ray diffraction (XRD) and electron probe microanalysis (EPMA). EPMA, which was carried out for the first time, indicates good controllability of the NC Ga/(In +Ga) ratio using this synthesis method. Raman spectroscopy reveals that CuInSe2 NCs are a mixture of chalcopyrite and sphalerite with disordered cations, whereas CuGaSe2 NCs are purely chalcopyrite. The lattice parameters determined from XRD were found to deviate from those calculated using Vegard's law for all compositions. Hence, it can be deduced that the lattice is distorted in the crystal. The optical and electrochemical band gap of CuInxGa1-xSe2 NCs increases as the Ga content increases. The energy band gap deviates from the theoretical values, which could be related to the contribution from cation disordering and strain. These results help to tailor the opto-electrical properties of semiconductors, which inherently depend on the crystalline quality, strain and composition.


Publication metadata

Author(s): Ahmadi M, Pramana SS, Boothroyd C, Lam YM

Publication type: Article

Publication status: Published

Journal: Nanotechnology

Year: 2017

Volume: 28

Issue: 4

Print publication date: 27/01/2017

Online publication date: 20/12/2016

Acceptance date: 14/11/2016

Date deposited: 29/08/2017

ISSN (print): 0957-4484

ISSN (electronic): 1361-6528

Publisher: Institute of Physics Publishing

URL: https://doi.org/10.1088/1361-6528/28/4/045708

DOI: 10.1088/1361-6528/28/4/045708


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