Supplementary Information
Unveiling the Influence of Phonon Anharmonicity on Raman Spectra of Cu 2ZnSn(S,Se)4
Polycrystalline Thin Films: a Groundbreaking Computational Study
Yurii A. Romaniuk*1,2, Ivan S. Babichuk*2,3, Vadim V. Koroteev2, Volodymyr O. Yukhymchuk2,
Volodymyr M. Dzhagan2, Sergiy V. Virko2, Mykola O. Semenenko2, Maksym O. Stetsenko4,5,
Anton Tiutiunnyk*6, Laura M. Pérez7 and David Laroze8
1
State Key Laboratory of Precision Spectroscopy, Department of Physics, East China Normal University, 200062,
Shanghai, P.R. China
2
V. Ye Lashkaryov Institute of Semiconductor Physics, NAS of Ukraine, 03680, Kyiv, Ukraine
3
School of Mechanical and Automation Engineering and Jiangmen Key Laboratory of Intelligent Manufacturing of
Polymer Materials, Wuyi University, 529020, Jiangmen, P.R. China
4
School of Science, Westlake University, Hangzhou, Zhejiang 310024, P.R. China
5
Institute of Natural Sciences, Westlake University, Hangzhou, Zhejiang 310024, P.R. China
6
Departamento de Física, FACI, Universidad de Tarapacá, 1000000, Arica, Chile
7
Departamento de Ingenieria Industrial y de Sistemas, Universidad de Tarapacá, 1000000, Arica, Chile
8
Instituto de Alta Investigación, Universidad de Tarapacá, 1000000, Arica, Chile
* Corresponding authors: romanyuk_yu@ukr.net, ivan@szu.edu.cn, tyutyunnyk.a.m@uta.cl
S1
Fig. S1. The surface morphology (a-d), cross-section (e, f), elements distribution (g, h) and spectra
(i, j) of Cu2ZnSnS4 and Cu2ZnSnSe4 thin films, respectively. Diffraction patterns of the CZTS and
CZTSe thin films (k). Absorption spectra as (αhν)2 = f(hν) of the CZTSe and CZTS thin films (l).
S2
Fig. S1 shows the SEM surface morphology images of Cu2ZnSnS4 (CZTS) and Cu2ZnSnSe4
(CZTSe) films obtained by the two- and one-step process, respectively, and their elemental
mapping with energy-dispersive X-ray (EDX) spectroscopy. The CZTS in Figs. S1a and S1b film
contains granules with a size ranging from 0.5 to 1 μm. Similar sizes were obtained for CZTSe
films (Figs. S1c and S1d). The thicknesses, from the cross-section, of all the films were evaluated
to be ∼1–2 μm on average and Mo ∼1 μm (Fig. S1e, f). Composition distribution (Figs. S1g and
S1h) and ratios of the precursors in the films were measured by EDX from a large area
(50×50 μm2), and the averaged values are shown in the EDX spectra (Figs. S1i and S1j). It should
be noted that CZTSe film has a more orderly distribution of elements by rotation than the CZTS
film. To some extent, this is reflected in the element of the composition and spectra of absorption.
The CZTS film was Cu-poor and Zn-rich. S and Sn concentrations negligibly differ from the
idealized parameters (25.0:12.5:12.5:50). The composition of CZTSe film for Cu- and Zn- was
rich, while for S and Sn- and Se- was poor. The crystal structure of our films was analyzed using
XRD (Fig. S1k). The intense peak positioned at ∼27° and ∼28° (112 planes) indicates the
orientation of the kesterite structure for CZTSe 1,2 and CZTS 3,4, respectively. Other diffraction
peaks, labeled in Fig. S1k, also correspond to the CZTSe and CZTS kesterite structure that
belongs to a tetragonal system according to JCPDS-52-0868 (CZTSe) and JCPDS 26–0575
(CZTS) databases. The intense peak of about ∼40° can be attributed to the Mo layer 5. The optical
band gap (Eg) of the CZTSe and CZTS films was determined from the obtained transmission and
reflection 6. The Eg values were 1.0 eV for CZTSe and 1.38 eV for CZTS (Fig. S1l) 7. A deviation
from the stoichiometry of the component composition causes a significant deviation from the
value of 1.5 eV in CZTS.
S3
Fig. S2. A schematic representation of the CZT(S,Se) unit cell for kesterite (KS) (a), stannite (ST)
(b) and PMCA (c) structures.
Table S1. Space group 𝐼4̅ = 𝑆24 (point group 𝑆4 )
S4
A
E
1
S4
1
C2
1
S 43
1
Rz
 xx +  yy ;  zz
B
1
-1
1
-1
Tz
 xx −  yy ;  xy
E1
1
1
i
-i
-1
-1
-I
i
1
1
1
-1
1
1
1
-1
E2
{ 2 ( B)}+
{ 2 ( E1, 2 )}+
(Tx, Ty), (Rx, Ry)
( xz ,  yz )
Table S2. Comparison of DFT calculated and experimental lattice parameters (in Å) of the KS,
ST and PMCA structures of CZTS and CZTSe.
Ref.8
Our
DFT
Exp.
CZTS
KS
ST
PMCA
a
c
a
c
a
c
5.443 10.786 5.403 10.932 5.40 10.942
CZTSe
KS
ST
PMCA
a
c
a
c
a
c
5.717 11.378 5.696 11.455 5.692 11.463
5.472 10.932 5.466 10.924 5.47 10.95
5.734 11.436 5.733 11.464 5.73 11.46
5.432 10.840 5.426 10.81
5.680 11.360 5.688 11.353
S4
11
1
Table S3. Space groups 𝐼4̅2𝑚 (𝐷2𝑑
) and 𝑃4̅2𝑚 (𝐷2𝑑
) (both with point group 𝐷2𝑑 )
D 2 d = Vd
E
2 S4
C2
A1
2 d
1
2C 2'
1
1
1
1
A2
B1
1
1
1
-1
1
1
-1
1
-1
-1
Rz
B2
1
-1
1
-1
1
Tz
 xy
E
2
0
-2
0
0
(Tx, Ty); (Rx, Ry)
( xz ,  yz )
{ E2 ( g )}+
3
-1
3
1
1
{E} →
A1  B1  B2
2
 xx +  yy ;  zz
 xx −  yy ;
Table S4. Parameters used at the fitting of theoretical dependences to experimental spectra CZTS
and CZTSe (All energy parameters are taken in arbitrary units, i.e., 𝐴𝑝 ≡ 𝐴𝑝 /𝑀, 𝛤 ≡ 𝛤/𝑀, etc.
where 𝑀 = 100 cm-1 is a scale factor).

𝛤
p
p
R2 c
c
𝑀1𝑝 : 𝑀2𝑝 : 𝑀3𝑝
Ap
CZTS, FR-1
0.028
0.003
0.05
-0.25
1.8
0.015
0.04
0.04:0.04:0.001
CZTS, FR-2
0.03
0.003
0.04
0.14
1.35
0.01
0.05
0.03:0.03:0.001
CZTSe, FR-3
0.04
0.002
-0.04
0.04
0.91
0.025
0.04
0.05:0.05:0.001
CZTSe, FR-4
0.062
0.003
-0.02 -0.25
1.18
0.015
0.05
0.05:0.05:0.001
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