Nanopowders of copper indium diselenide were produced with five different organic solvents: ethylenediamine, triethanolamine, oleylamine, oleic acid, and polyetheramine. We successfully synthesized pure CIS nanopowders at a temperature of 240°C at three different durations of 10 h, 20 h, and 40 h with a one-step process. This shorter time method offers important cost advantages in manufacturing. Polyetheramine and oleic acid were used for the first time in literature for CIS synthesis in an autoclave.
Copper indium diselenide (CIS), CuInSe2, is one of the most important semiconductor materials used in thin film photovoltaic (PV) cells. CIS is becoming a promising candidate material for solar cell applications due to its high optical absorption coefficient, suitable direct band gap energy, and long term stability [
In this study, we used the solvothermal method based on dissolving metals or metal salts with organic solvents in an autoclave at low temperatures with a single-step process. Nanopowders were produced with five different organic solvents: ethylenediamine, triethanolamine, oleylamine, oleic acid and polyetheramine. We successfully synthesized pure CIS nanopowders at a temperature of 240°C, at three different durations of 10 h, 20 h, and 40 h with a one-step process.
All chemicals (A. Aesar Co.) were used as received without further purification. Copper chloride (CuCl2 anhydrous 98%), indium chloride (InCl3 anhydrous 98%), gallium chloride (GaCl3 anhydrous 99%), and selenous acid (H2SeO3 anhydrous 98%) were used as precursors and anhydrous ethylenediamine, triethanolamine, oleylamine, polyetheramine, and oleic acid were used as organic solvents.
In the experimental process, CuCl2, InCl3, GaCl3, and H2SeO3 (chemical mixture) were weighed according to the stoichiometric ratio of 1 : 0.7 : 0.3 : 2 in an argon filled glove box. All samples were prepared separately according to solvent characteristics.
For preparation of sample with anhydrous ethylenediamine, 17.5 ml anhydrous ethylenediamine and 2.5 ml ethanol were added to chemical mixture in a glove box and dissolved for 30 minutes with magnetic stirring and then held for 5 minutes in an ultrasonic bath. Sample was loaded into a Teflon-lined stainless steel autoclave with 45 ml capacity. The autoclave was sealed and maintained at 240°C for 10 h, 20 h, and 40 h in an electric oven. After the reaction, the autoclave was allowed to cool to room temperature. CIS nanoparticles in a black colored ethylenediamine organic solution were subject to centrifugation at 6000 rpm repeated four times and rinsed with distilled water and ethanol to remove the byproducts. The final black slurry was dried at 80°C for 8 hours in a drying oven.
For preparation of triethanolamine sample, 18 ml ethanol, 2 ml distilled water, and TEA were added to chemical mixture in a glove box and dissolved for 30 minutes with magnetic stirring before keeping in ultrasonic bath for 5 minutes. Sample was loaded into a Teflon-lined stainless steel autoclave with 45 ml capacity. The autoclave was sealed and maintained at 240°C for 10 h, 20 h, and 40 h in an electric oven. After the reaction, the autoclave was allowed to cool naturally to room temperature and CIS nanoparticles, in black color ethylenediamine organic solution, were collected after centrifugation at 8000 rpm repeated 4 times and rinsed with distilled water and ethanol to remove byproducts. The final black slurry was dried at 80°C for 8 hours in a drying oven.
For preparation of oleylamine sample, 20 ml oleylamine was added to chemical mixture in a glove box and dissolved for 30 minutes with magnetic stirring before keeping in ultrasonic bath for 5 minutes. Sample was loaded into a Teflon-lined stainless steel autoclave with 45 ml capacity. The autoclave was sealed and maintained at 240°C for 10 h, 20 h, and 40 h in an electric oven. After the reaction, autoclave was allowed to cool naturally to room temperature and CIS nanoparticles, in black color ethylenediamine organic solution, were collected after centrifugation at 8000 rpm repeated 4 times and rinsed with acetone to remove byproducts. The final black slurry was dried at 80°C for 24 hours in a drying oven.
For preparation of oleic acid sample, 20 ml oleic acid, 2 ml ethanol, and 1 ml distilled water were added to chemical mixture in a glove box and dissolved for 30 minutes with magnetic stirring before keeping in ultrasonic bath for 5 minutes. Sample was loaded into a Teflon-lined stainless steel autoclave with 45 ml capacity. The autoclave was sealed and maintained at 240°C for 10 h, 20 h, and 40 h in an electric oven. After the reaction, autoclave was allowed to cool naturally to room temperature and CIS nanoparticles, in black color ethylenediamine organic solution, were collected after centrifugation at 8000 rpm repeated 4 times and rinsed with acetone to remove byproducts. The final black slurry was dried at 80°C for 24 hours in a drying oven.
For preparation of 20 ml polyetheramine sample 2 ml ethanol and 1 ml distilled water were added to chemical mixture in a glove box and dissolved for 30 minutes with magnetic stirring and then for 5 minutes at ultrasonic bath. Sample was loaded into a Teflon-lined stainless steel autoclave with 45 ml capacity. The autoclave was sealed and maintained at 240°C for 10 h, 20 h, and 40 h in an electric oven. After the reaction, autoclave was allowed to cool naturally to room temperature and CIS nanoparticles, in black color ethylenediamine organic solution, were collected after centrifugation at 8000 rpm repeated 4 times and rinsed with distilled water, acetone, and ethanol mixture to remove byproducts. The final black slurry was dried at 80°C for 24 hours in a drying oven.
The crystal structure was characterized by X-ray diffraction (XRD). The morphology and size of synthesized CIS nanoparticles were characterized by scanning electron microscopy (SEM) equipped with an EDAX.
The oleylamine plays several roles during the synthesis of CIS. It enables control of the growth rate of the nanoparticles during reactions by forming a liquid-metal complex. It plays the role of a capping agent for the nanoparticles. It is thought to reduce the reactivity between Cu, In, Ga, and Se reactants [
XRD pattern of synthesized CIS powder at 240°C for 10, 20, and 40 hours with oleylamine solvent.
Figure
Pure tetragonal CIS powder was synthesized during the reaction at 10 hours; when time was increased to 20 hours a second phase tetragonal CuGaSe was observed. At 40 hours process time, the peak intensity was lower and CuGaSe phase disappeared. According to Hahn et al. [
To investigate the morphological properties of CIS nanoparticles, SEM images from the synthesized CIS powder were gathered and provided in Figure
SEM micrographs of synthesized CIS powder at 240°C for (a) 10 h, (b) 20 h, and (c) 40 h with oleylamine solvent.
In Figure
XRD pattern of synthesized CIS powder at 240°C for 10, 20, and 40 hours with triethanolamine solvent.
In this study, based on XRD data from Figure
SEM micrographs of synthesized CIS powder at 240°C for (a) 10 h, (b) 20 h, and (c) 40 h with triethanolamine solvent.
CIS nanoparticles were synthesized with oleic acid as a solvent, which has a similar molecular structure to different functional group as Hahn et al. [
XRD pattern of synthesized CIS powder at 240°C for 10, 20, and 40 hours with oleic acid.
SEM micrographs of synthesized CIS powder at 240°C for (a) 10 h, (b) 20 h, and (c) 40 h with oleic acid.
At 10 h process time, three different phases were observed. They were tetragonal CuGaInSe, tetragonal CuInSe2, and tetragonal Cu3Se2 phases. At 20 h process, pure tetragonal CIS phase was observed. At 40 h process, tetragonal CIS particles were observed with lower intensity compared to 20 h process. Hahn et al. [
Polyetheramine is a rare solvent with double amine-capped polymer with a high boiling point resulting in strong chelation. Wang et al. [
Figure
XRD pattern of synthesized CIS powder at 240°C for 10, 20, and 40 hours with polyetheramine.
SEM micrographs of synthesized CIS powder at 240°C for (a) 10 h, (b) 20 h, and (c) 40 h with polyetheramine.
EDA is most preferred solvent for synthesizing CIGS, CIS powders with solvothermal method. Zhang et al. [
The tetragonal CGS, hexagonal GaSe, Se and CuSe phases with 150–200 nm agglomerated particles were observed at processing time of 10 h, based on Figures
XRD pattern of synthesized CIS powder at 240°C for 10, 20, and 40 hours with ethylenediamine.
SEM micrographs of synthesized CIS powder at 240°C for (a) 10 h, (b) 20 h, and (c) 40 h with ethylenediamine.
Five different solvents such as oleylamine, oleic acid, triethanolamine, polyetheramine, and ethylenediamine were successfully used to synthesize tetragonal CIS powders with solvothermal method in an autoclave in the same conditions. It has been found that oleylamine is the best solvent based on the X-ray data from processing at 240°C for 10, 20, and 40 hours. CIS phase was successfully synthesized using five different solvents. According to results at these processing conditions, best desirable properties were obtained in this order: (1) oleylamine (10 hours), (2) triethanolamine (20 hours), (3) oleic acid (20 hours), (4) polyetheramine (10 hours), and (5) ethylenediamine (20 hours). Polyetheramine and oleic acid were used for the first time in literature for CIS synthesis in an autoclave. Other methods were studied in the literature; the chemical reaction occurs in a three-necked flask which takes much long time for a successful synthesis.
The authors declare that they have no conflicts of interest.