CZTSxSe1−x nanocrystals: Composition dependent method of preparation, morphological characterization and cyclic voltammetry data analysis

In this article, synthesis procedures of preparation of copper zinc tin sulpho-selenide (CZTSxSe1−x) alloy nanocrystals and the data acquired for the material characterization are presented. This data article is related to the research article doi: http://dx.doi.org/10.1016/j.solmat.2016.06.030 (Jadhav et al., 2016) [1]. FTIR data have been presented which helped in confirmation of adsorption of oleylamine on CZTSxSe1−x. Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) data have been presented which have been used to reveal the morphological details of the nanocrystals. The Energy dispersive X-ray analysis (EDAX) based elemental mapping data has been presented to confirm the elemental composition of nanocrystals. Procedure for the preparation of CZTSxSe1−x based working electrode for the CV measurements have been given. The summary table for the optical, electrochemical band gaps, valance and conduction band edges as a function of composition are listed for the ready reference.


a b s t r a c t
In this article, synthesis procedures of preparation of copper zinc tin sulpho-selenide (CZTS x Se 1 À x ) alloy nanocrystals and the data acquired for the material characterization are presented. This data article is related to the research article doi: http://dx.doi.org/10. 1016/j.solmat.2016.06.030 (Jadhav et al., 2016) [1]. FTIR data have been presented which helped in confirmation of adsorption of oleylamine on CZTS x Se 1 À x . Transmission electron microscopy (TEM), Field emission scanning electron microscopy (FESEM) and atomic force microscopy (AFM) data have been presented which have been used to reveal the morphological details of the nanocrystals. The Energy dispersive X-ray analysis (EDAX) based elemental mapping data has been presented to confirm the elemental composition of nanocrystals. Procedure for the preparation of CZTS x Se 1 À x based working electrode for the CV measurements have been given. Detail FTIR data analysis has been presented for the adsorbed oleylamine molecules on the CZTS x Se 1 À x nanocrystals.
AFM, TEM and FESEM data have been used to demonstrate composition independent morphological similarity of CZTS x Se 1 À x . The EDAX mapping data have been used to confirms the absence of phase segregation and formation of uniform composition.
Composition dependent band edge positions have been presented in tabular form which will act as a guideline to design novel heterojunction photovoltaic device by band alignment engineering.

Data
The data given in this data article are in the form of seven figures and one table. It describes detail synthesis, characterization and procedure followed for cyclic voltammetry investigation of CZTS x Se 1 À x (x ¼0-1) nanocrystals. TEM data have been presented for highlight the morphology and size distribution. The topography has been recorded by FESEM and AFM image analysis. The EDAX spectra give the details about composition and stoichiometry. Uniform distributions of the constituent elements are seen in the elemental mapping images. The adsorption of capping agent, oleylamine has been confirmed by FTIR data. The procedure for the preparation of working electrode for the electrochemical investigation is described in detail.

Synthesis setup and CZTS x Se 1 À x alloy nanocrystals synthesis
The Synthesis of the CZTS x Se 1 À x (x ¼0-1) nanocrystals carried out using hot injection method suggested by Agrawal and Riha et al. [2,3]. A typical synthesis setup used in present investigation [1] is shown in Fig. 1. The sequence of addition is marked as red-arrows. Weighed amount of all the constituents (salts in oleylamine (OLA)) are first transferred into the three necked flask, mounted on heating mantle, having temperature controller. Upon heating to 130°C with constant stirring, all the metal complexes dissolved and from brown transparent solution. Temperature is raised further to 225°C (Refer Fig. 1(A)) and into it freshly prepared S/Se in OLA solution was added, which leads to black color product (Refer Fig. 1(C)).

Drop-casting of films on the working electrode
The electrochemical measurements on the samples have been done on CZTS x Se 1 À x coated golddisk working electrode (2 mm diameter). For that, the sample was applied on the electrode by method of drop-casting. For that, the electrode was mounted vertically in a desiccator. 75 μL dispersion of nanocrystals in dichloromethane was applied carefully onto the electrode surface. The drop was allowed to dry by the help of mild vacuum (diaphragm vacuum pump) for 15 min. This helps solvents to evaporate quickly and form a film on the electrode surface. Adhesion of the film was found to be good and did not show any tendency to fall down or fouling in the solvent, during the measurements. From the weight of the loading, area of the electrode and density of samples, the thickness of the films were estimated and found to be in the range 58 μm. Such modified electrodes were used as prepared without any post annealing.
3. Characterization of CZTS x Se 1 À x alloy nanocrystals 3.1. FTIR spectroscopy data on CZTS Sample Fig. 2(A) shows the FTIR spectra recorded on CZTS nanocrystals powder samples and its comparison with a neat oleylamine sample (coordinating solvent). The band at 3372 cm À 1 and 3292 cm À 1 in OLA sample is attributed to the asymmetric and symmetric stretching from primary NH 2 group [4]. These bands are replaced by new band at 3170 cm À 1 in CZTS samples those matched with stretching vibration from the secondary amine group. This observation is explained on the basis of change in bond order during the adsorption. Similarly, the intensity of bending vibrations at 795 cm À 1 for the NH 2 in OLA is decreased and shifted to 802 cm À 1 in CZTS sample. Intensity of the CH 3 and corresponding to C-C bending vibrations at 1465 cm À 1 and 722 cm À 1 are decreased in case of OLA adsorbed on CZTS. In both the cases, neat OLA and OLA on CZTS show the C-H symmetric and asymmetric stretching vibrations [4] because of the methylene and methyl group at 2923 cm À 1 and 2852 cm À 1 . The bending vibration due to C-N at 1071 cm À 1 is broadened in case of OLA with CZTS. In CZTS sample a strong band at 605 cm À 1 is observed which corresponds to metal nitrogen stretching mode [5]. Over all, from the FTIR data analysis, co-ordination of OLA with CZTS nanocrystals is confirmed. Fig. 2(B) shows the similar bands in case of rest all the composition. Fig. 3 shows the TEM micrographs for the CZTS x Se 1 À x alloy nanocrystals for varied composition. Fig. 3(A) and (D) represents the low resolution and high resolution images for x¼ 0.17 respectively, Fig. 3(B) and (E) represent the low and high resolution images for x¼ 0.42 respectively, Fig. 3(C) and (F) represents the low and high resolution images for x ¼0.74 respectively. The TEM images for the x ¼1 and x ¼0 are shown in [1]. For all compositions faceted morphology with polyhedron shapes having size ranging from 10 to 30 nm are observed.       EDAX based elemental mapping. It is presented in Fig. 7(A-E). The inset of Fig. 7(A-E) shows the bar chart for stoichiometry as element vs. atomic % (stoichiometry). Mapping data underlines uniform stoichiometric distribution in the samples. Table 1 summarizes the data for optical band gaps form UV-Visible spectroscopy and electrochemical band gaps from cyclic voltammetry. From the voltammetric measurement the band edge parameters viz. valance band and conduction band edge were estimated vs. NHE and local vacuum respectively. Along with band edge parameters the crystals structure parameters like lattice constants and d-spacing calculated from X-ray diffraction pattern also presented in Table 1.