Original Research Paper
Synthesis and properties of Cu
2
(Fe
x
Zn
1x
)SnS
4
nanocrystals by
microwave irradiation assisted solvothermal method
Wei Wang
a
, Honglie Shen
a,b,
⇑
, Jieyi Chen
a
, Weilong Chen
a
, Xiancong He
c
a
College of Materials Science and Technology, Nanjing University of Aeronautics and Astronautics, 29 Yudao Street, Nanjing 210016, China
b
Key Laboratory for Intelligent Nano Materials and Devices of Ministry of Education, Jiangsu Provincial Key Laboratory of Materials and Technology for Energy Conversion,
Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China
c
College of Materials Engineering, Nanjing Institute of Technology, Nanjing 211167, China
article info
Article history:
Received 18 July 2014
Received in revised form 7 October 2014
Accepted 10 October 2014
Available online 22 October 2014
Keywords:
Cu
2
(Fe
x
Zn
1x
)SnS
4
Nanocrystals
Microwave irradiation assisted
solvothermal method
Band gaps
abstract
In this paper, Cu
2
(Fe
x
Zn
1x
)SnS
4
nanocrystals were synthesized by a microwave irradiation assisted
solvothermal method. The properties of Cu
2
(Fe
x
Zn
1x
)SnS
4
nanocrystals were studied by X-ray diffrac-
tion, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and
UV–vis spectroscopy. The results showed that as-synthesized Cu
2
(Fe
x
Zn
1x
)SnS
4
nanocrystals had a single
phase and stoichiometric composition. The average crystalline size increased with increasing x. More-
over, the band gaps of Cu
2
(Fe
x
Zn
1x
)SnS
4
nanocrystals decreased with increasing x.
Ó 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder
Technology Japan. All rights reserved.
1. Introduction
In recent years, the energy crisis has forced people to find clean
and renewable energy. Solar energy is one of the most ideal renew-
able energy. Solar cells can convert sunlight to electricity. How-
ever, the cost of traditional crystalline silicon solar cells is high.
As a result, the low-cost and novel solar cell materials such as
Cu(In,Ga)(S,Se)
2
,Cu
2
ZnSnS
4
(CZTS), and Cu
2
FeSnS
4
, are attracting
widespread interest. Particularly, CZTS has garnered considerable
interest, which contains earth-abundant, low-cost, and nontoxic
elements and retain the similar structure to Cu(In,Ga)(S,Se)
2
. More-
over, Cu
2
ZnSnS
4
has an optical band gap (1.5 eV) and a large
absorption coefficient (>10
4
cm
1
) [1]. Furthermore, according to
the Shockley–Queisser photon balance calculations, the theoretical
limit for Cu
2
ZnSnS
4
thin film solar cells is nearly 32.2% [2].
Various methods have been used to prepare Cu
2
ZnSnS
4
thin
films for solar cells. Shin et al. [3] reported that 8.4% efficiency Cu
2
ZnSnS
4
solar cell was fabricated by co-evaporation deposition
method. However, the deposition technique generally requires
high vacuum system increasing preparation cost. In contrast,
non-vacuum based approaches can provide low-cost routes to
Cu
2
ZnSnS
4
solar cells. These non-vacuum based approaches
include spray pyrolysis [4], electrodeposition [5], sol–gel method
[6], hydrazine-based processing [7], nanocrystals-based approach
[8], etc. Among these non-vacuum methods, Wang et al. [7] fabri-
cated Cu
2
ZnSn(S,Se)
4
thin film solar cells with 12.6% by hydrazine-
based processing. However, hydrazine is highly toxic and reactive,
and requires extreme caution during handling and storage. Xin
et al. [8] reported a molecular precursor approach using non-toxic
solvent DMSO to prepare CZTS thin film and resulting in a solar cell
with 8.3% efficiency. Recently, nanocrystals-based approach has
obtained more and more attention, due to its many advantages.
This method can easily to fabricate solar cells at a large scale com-
bined with roll-to-roll, printing, and casting. Moreover, this
method can control phase formation because it enables phase for-
mation to occur prior to film deposition. Miskin et al. [9] prepared
9% efficiency Cu
2
ZnSn(S,Se)
4
solar cells from selenized nanoparti-
cles inks. This method could avoid using high toxic hydrazine,
but is required to prepare high quality Cu
2
ZnSnS
4
nanoparticles.
At present, the main methods to prepare Cu
2
ZnSnS
4
nanoparticles
include hot injection [10], solvothermal [11], mechanochemical
[12], and microwave irradiation [13]. Among these methods,
microwave irradiation offers great advantages such as high reac-
tion rate, higher yield and better reproducibility of product.
At present, many researchers have indicated that Se incorpora-
tion is an effective way to tailor the band gap and improve solar
cells efficiency [14]. However, the approaches to tune band gap
http://dx.doi.org/10.1016/j.apt.2014.10.009
0921-8831/Ó 2014 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
⇑
Corresponding author at: College of Materials Science and Technology, Nanjing
University of Aeronautics and Astronautics, 29 Yudao Street, Nanjing 210016, China.
Tel./fax: +86 25 52112626.
E-mail address: hlshen@nuaa.edu.cn (H. Shen).
Advanced Powder Technology 26 (2015) 275–279
Contents lists available at ScienceDirect
Advanced Powder Technology
journal homepage: www.elsevier.com/locate/apt