Synthesis CuInSe 2 ( CISe ) Thin Films Prepared from Metal-Ethanolamine Complex Compound

CuInSe2 (CISe) thin film was successfully fabricated from copper and indium salts with ethanolamine as precursors. All of these precursors were dissolved and formed complex compounds with ethanolamine simultaneously which deposited on soda lime glass by spin coating at 200 rpm, followed by heat treatment in the ambient atmosphere at 200C for 120 minutes and finally selenization at 550C using selenium pellets under Ar (95%) + H2 (5%) for 120 minutes to fabricate CISe thin film. Reaction mechanism, structure, morphology and chemical composition also reported in this work. © 2017 Tim Pengembang Journal UPI Article History: Received 03 May 2017 Revised 31 May 2017 Accepted 16 Jun 2017 Available online 01 Sep 2017 ____________________ Keyword: Synthesis CuInSe2, Ethanolamine as precursors, Complex compounds, Selenium pellets. Indonesian Journal of Science & Technology Journal homepage: http://ejournal.upi.edu/index.php/ijost/ Indonesian Journal of Science & Technology 2 (2) (2017) 191-196 Ersan Y. Muslih, et.al. Synthesis CuInSe2 (CISe) Thin Films Prepared from... | 192 DOI: http://dx.doi.org/10.17509/ijost.v2i2 pISSN 2528-1410 eISSN 2527-8045


INTRODUCTION
CuInSe2 (CISe) is an ideal material for thin film solar cell application due to has optimum band gap (1.01 eV) and high absorption coefficient (105 cm-1) (Shay et al., 1973;J. Araujo et al., 2007).CISe thin films could be prepared by vacuum and nonvacuum methods.However, non-vacuum process such as chemical process is preferable due to low cost but still get high efficiency (Yin Liu et al., 2012).Although chemical process is preferable, this method using harmful solvents such as hydrazine and pyridine (C.J. Hibberd et al., 2010).Besides that, chemical process could leaves carbon in the thin film as residue (Shanza et al., 2016).In this work, CISe thin film has been fabricated by chemical process using ethanolamine as a solvent, deposited by spin coating and followed by selenization.
There the purpose of this study wa to synthesized CuInSe2 this film.The material was prepare from copper and indium salts with ethanolamine as precursors

EXPERIMENTAL DETAIL 2.1. Materials and Methods
In this work, the precursor solution was made from 0.1 M of copper (from copper(II) acetate) and 0.1 M of indium (from indium(III) chloride) All components were dissolved in 30% ethanolamine (ETA) in ethanol.The solution and exhibited a blue color when using 1:1 Cu/In ratio.Moreover, 0.05 mL of precursor solution was deposited at 2000 rpm for 10 seconds on soda lime glass (SLG), which cleaned with acetone, ethanol, deionized water using ultrasonic for 15 minutes respectively and dried by nitrogen gas in order to eliminate contaminants further.Subsequently, deposited precursor was dried in tubular furnace at 200 o C for 120 minutes until black shinny color was appeared.Repeating the deposition and the heat treatment appropriately can get desirable film thickness.Finally, the CISe thin film obtained by selenization in tubular furnace at 550 o C using selenium pellets as selenium source under Ar (95%) + H 2 (5%) atmosphere for 120 minutes.After selenization, the sample was cooled to room temperature under natural cooling condition.

Characterization of CISe thin film
The morphology was observed by scanning electron microscopy (SEM, Hitachi S4800, Japan).The chemical composition of the films was analyzed by energy dispersive x-ray spectrometry (EDS, Horiba, Japan).The crystal structures were determined by x-ray diffraction (XRD, PANalytical MPD, Netherlands).The absorption spectra were recorded using a UV-Vis-NIR spectrophotometer (Varian Carry 5000, U.S.A).The electrical properties were examined by Hall-Effect measurements using a Van der Paw method (HMS-3000, Ecopia U.S.A.).

RESULTS AND DISCUSSION
In this work, ethanolamine (ETA) and metal ions such as copper and indium could form a complex compound due to ethanolamine has free electron pair which donated to metal ions and form a coordination or complex bonding where the ETA acts as ligands and the metal ions act as a center atom.Since the unique structure of ETA, thus ETA could act as a chelating agent which illustrated as Figure 1.
Moreover, at drying process, Cu-ETA and In-ETA complex compounds were decompossed under air atmosphere into metal oxide.Detailed reaction are After annealing at 550 o C under Ar (95%) + H2 (5%) atmosphere for 120 minutes, selenium was changed into vapor phase and then, some of Se vapor was react with metal oxide and H2 simultaneously.Se vapor reacts with metal oxide and H2 form metal selenide and H2Se respectively.Further, H2Se could react with metal oxide and form metal selenide either.Meanwhile, carbon as residue reacted with H2 became methane gas and removed from thin film.Finally, metal selenide such as CuSe and InSe were coalesced into CuInSe2 as a final product.In other hand, this reaction mechanism shows that H2 acts as catalyst and as carbon remover simultanously.Detailed reactions are Se (s) → Se (g) Se (g) + 2 MO (s) → MSe (s) + O2 (g) Se (g) + H2 (g) → H2Se  Moreover, scanning electron microscope (SEM) in Figure 3 shows that the morphology of precursor has smooth and tiny particles spread around the surface.Meanwhile, after annealing, shows the morphology, became larger and compact without shown hexagonal shape from copper was seen.It seems the reaction was going completely.
Organic residue was represented by carbon which existed in the thin film and could be determined by energy dispersive spectrometry (EDS) (see Figure 4).The spectrum shows the proof of carbon existence in the thin film before annealing.In addition to carbon, also could be seen the spectrums of chloride from metal salts, while oxygen could represent of either organic residue or metal oxide.However, after annealing, the EDS spectrums of carbon, chloride and oxygen spectrums were no longer seen in the thin film.It seems they have been removed successfully during annealing  EDS also could be used for determining the chemical composition of CISe thin film before and after annealing (see Table 1).Before and after annealing Cu/In ratio were 1.20 and 1.35 respectively.The slight enhancement of ratio probably due to diminished of indium in the thin film during annealing considering the melting point of indium (156 o C), which is below the annealing temperature.In other hand, copper is a stable material, thus during annealing it was not much diminished.

CONCLUSION
CuInSe2 (CISe) thin film has been synthesized successfully from metal salts and ethanolamine complex compounds by spin coating and followed by annealing method.Synthesis reaction mechanism of CISe also proposed in this work in order to explain whole process of synthesis from metal salts, complex compounds to CISe thin film.The structure of CISe thin film shows a tetragonal and matched with CISe standard.Moreover, CISe thin film has a suitable chemical composition with no more carbon or organic residue in the thin film.

Figure 2 .
Figure 2. XRD pattern of CuInSe2 thin film before (a) and after (b) annealing

Figure 3 .
Figure 3. SEM image of CISe before (a) and after (b) annealing