The chalcopyrite CuInSe2 thin film synthesized via a low temperature solid state reaction from CuSe and InSe powders was investigated using X-ray diffractomy (XRD), scanning electron microscope (SEM), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM), and UV-vis absorption spectroscopy. CuSe and InSe phases react and directly transform into CuInSe2 without the occurrence of any intermediate phase. The morphology of the newly formed CuInSe2 crystalline was close to that of the CuSe reactant particle based on the TEM results, which indicate that the solid state reaction kinetics may be dominated by the In3+ ions diffusion. The CuInSe2 thin film prepared from the solid state reaction did not use the selenide process; its band gap might reach 1.06 eV, which is competent and suitable to be used for a thin film solar cell light absorption layer.
For the new type-energy materials, the group IV quantum dot nanostructures for future generation solar cell applications [
High efficiency CIS solar cells are commonly prepared via the physical vapor deposition method [
A potential nonvacuum method for CIS formation is developed in this work. In the experiment, the CuSe and InSe powders are prepared by wet chemical method, which is one of the simplest and cheapest methods. The CIS thin film is thereafter obtained by spin coating from CuSe and InSe powders on the glass and then heated at 350°C for 3 h under nitrogen gas. The structure and the optical properties of the precursors and the CIS films are investigated and discussed.
The copper (I) chloride (99.99%, Alfa Aesar, Ward Hill, MA, USA) and indium (III) chloride (99.99%, Acros, Geel, Belgium) used were analytical grade reagents. Selenium powder (99.99%, Sigma-Aldrich, St. Louis, Missouri, USA) was a high purity reagent. Oleylamine (70%, Kanto Chemical Co., Inc., Tokyo, Japan), hexane (99%, Acros, Geel, Belgium), and ethanol (95%, Acros, Geel, Belgium) were used as received, without further purification. The deionized water (DI water) used in this work was obtained from EMD Millipore Corporation-Direct-Q 3 system (Billerica, MA, USA).
A typical synthesis of InSe particles was modified from Park et al.’s procedure [
The In2Se3 particles were synthesized by annealing the reaction mixture containing 0.45 mmol InCl3 and 0.70 mmol Se powder in 10 mL of OLA at 280°C under nitrogen gas for 5 h. The product was then centrifuged and washed with hexane, ethanol, and DI water several times and then dried at 80°C for 3 h in a vacuum oven.
The CuSe particles were synthesized by annealing the reaction mixture containing 0.50 mmol Se powder and 10 mL of OLA (OLA/Se) firstly mixed at room temperature, and the resulting solution was heated to 180°C. 0.46 mmol CuCl and was then quickly added into the hot OLA/Se solution; the reaction mixture was annealed at 220°C for 2 h under nitrogen gas. The product was then centrifuged and washed with hexane, ethanol, and DI water several times and then dried at 80°C for 3 h in a vacuum oven.
The Cu2Se particles were synthesized by annealing the reaction mixture containing 0.91 mmol CuCl and 0.50 mmol Se powder in 10 mL of OLA at 220°C for 2 h under nitrogen gas. All the products were then centrifuged and washed with hexane, ethanol, and DI water several times and then dried at 80°C for 3 h in a vacuum oven.
The CuInSe2 films were prepared using the as-prepared metal Se compounds as precursors in two reaction paths. In the reaction path A, the as-prepared InSe (0.25 mmol) and CuSe (0.25 mmol) were dispersed in ethanol and spin-coated on the glass with 500 rev. min−1 for 20 s in air, then dried at 100°C for 1 h to remove residual solvent. The glass was transferred into closed graphite box and heated at 350°C for 3 h under nitrogen gas. In the reaction path B, the as-prepared In2Se3 (0.25 mmol) and Cu2Se (0.25 mmol) were also dispersed in ethanol and spin-coated on the glass with 500 rev. min−1 for 20 s in air, then dried at 100°C for 1 h to remove residual solvent. The glass was transferred into closed graphite box and heated at 350°C for 3 h under nitrogen gas. The experimental parameters were summarized in Table
Experimental conditions and results.
No. | Materials | Precursors ratio | Measured by EDS |
Time (h) | Temp (°C) | Products |
---|---|---|---|---|---|---|
1a | InCl3 + Se | 1 : 1 | 0 : 1 : 1.06 | 5 | 220 | InSe |
2a | InCl3 + Se | 2 : 3 | 0 : 2 : 3.01 | 5 | 280 | In2Se3 |
3a | CuCl + Se | 1 : 1 | 1 : 0 : 0.99 | 2 | 220 | CuSe |
4a | CuCl + Se | 2 : 1 | 1.74 : 0 : 1 | 2 | 220 | Cu2Se |
5b | InSe + CuSe | 1 : 1 | 1 : 0.79 : 1.86 | 3 | 350 | CuInSe2 |
6b | In2Se3 + Cu2Se | 1 : 1 | 1 : 1.32 : 1.94 | 3 | 350 | CuInSe2 + In2Se3 |
bThe precursors were prepared by samples no. 1~4 and reaction through low temperature solid state reaction.
The X-ray powder diffraction (XRD, operating at 8 kV) patterns of the as-prepared samples were recorded on Shimadzu XRD-6000 X-ray diffractometer (Kyoto, Japan) with Cu K
The phase and crystallographic structure of the as-prepared metal Se compounds were determined by XRD. Figure
XRD patterns of as-prepared (a) InSe [
XRD patterns obtained from the annealed thin film made by (a) CuSe and InSe and (b) Cu2Se and In2Se3.
Figure
Figure
Various images of the as-prepared CIS thin film from path A: (a) cross-sectioned SEM image for the as-synthesized CIS before annealing and (b) that after annealing, (c) LR-TEM, and (d) HR-TEM and SAED (the insert) images for the as-prepared CIS.
Hsiang et al. [
TGA curves of (a) CuSe, (b) InSe, (c) Cu2Se, (d) In2Se3, and (e) CIS particles prepared by the reaction path A or B via solid state reaction.
Furthermore, Figure
The (a) UV-vis absorption spectrum and (b) Raman spectrum of CIS thin films synthesized from the reaction path A.
In this work, CIS thin film is successfully fabricated by using CuSe and InSe binary precursors via a low temperature solid state reaction. The XRD results indicate that CIS thin film has a chalcopyrite structure with good crystallinity, which exhibits (112) prefer orientation. Particularly, CIS thin film can be preferably obtained by path A with the reaction of CuSe + InSe → CuInSe2 at relatively low temperature (350°C) and short preparation time (3 h). Besides, the weight loss indicated by TGA pattern is only 1.5% at 600°C. The value of band gap for the as-prepared CIS is calculated to be 1.06 eV, which demonstrates that this material is suitable to be used for a thin film solar cell light absorption material. Its good absorption in the visible light region also suggests that such photovoltaic material is promising for sustainable energy related applications.
The authors thank the National Sciences Council of Taiwan for the financial support, Grant nos. NSC 102-2113-M-024-001 and 101-2321-B-006-01.