Aqueous Phase Synthesis of CuIn Alloy Nanoparticles and Its Application for CIGS Solar Cell

Among various low cost solar cells with high efficiency, CIGS (Cu(In,Ga)Se₂) type solar cell shows attractive performances. These CIGS type solar cell is synthesized by gas phase method or liquid phase reduction method in organic solvents. However, in the case of former, productivity is relatively low, since vaporizing temperature of three or more elements is extremely different, which read the large amount of waste of resources. On the other hand, in the case of later, synthesis costs become increase because of the use of organic solvents. Thus, to decreasing the cost of CIGS type solar cell, synthesis method with high recovery rate and without the using of organic solvents is required.

Until now, we reported that the synthesis of uniform and well crystallized alloy nanoparticles, such as Pd₂₀Te₇ and Bi₂Te₃ by restrict controlling the homogenization of metallic complexes in the aqueous solution under room temperature [1]. In this method, reduction rate of the metal species can be controlled under the room temperature, nevertheless ternary, or more, alloy nano materials with uniform and well crystallized structure was not synthesized until now.

Therefore, in this study, CI nanoparticles were synthesized by obeying the calculation results and reduction potential measurements. CIS semiconductor was tried to synthesize through selenided reaction of CI nanoparticles synthesized. Solar cell ability was also investigated.

Metallic complexes in the aqueous solution was restricted to homogenized species by utilizing the theoretical calculation method using the critical stability constants. Detailed calculation procedure was summarized in Ref. 1. Amine-based and/or carboxyl-based complexing reagent, were used for the complex reagents. Reduction potential of Cu (and/or In) complexes was measured, and synthesized materials were analyzed by XRD.

Calculation was performed for various system, such as the Cu-NO₃-OH-glycine system (dissolution of Cu(NO₃)₂ and glycine). By obeying the calculation results and also electrochemical potential measurement, various copper complexes was successfully restricted to single species, such as [(Cu²⁺)(Gly)₂], at the pH range over 10, and relationship between stability constants of complex reagents and reduction potential were summarized. As a results, CuIn nanoparticles can be successfully synthesized.

CuInSe semiconductor materials were also synthesized by gas phase selenided reaction of the CuIn thin film on the substrate. XRD mesurments shows that synthesized materials were single phase of CuInSe alloy. Synthesized CuInSe thin film on the substrate shows the voltage under the irradiation of light. Thus, by using this easy methods, solar cell can be constructed.

This work was supported by the Grant-in-Aid for Challenging Exploratory Research (No. 25550085).

References: [1]H. Takahashi, et.,al; Applied Catalysis A: General 392, 80-85 (2011)