Formation of CuInSe2 Printable Solar Cell Using Aqueous Phase Synthesized CuIn Alloy Nanoparticles

Actualization of environmental problems has induced the utilization of natural energy, such as solar energy. On the other hand, it is true that minimum energy payback time of Si solar cell is long, and dramatic improvement of Si based solar battery’s efficiency is not easy since its efficiency come closed to theoretical value. Therefore, various type solar battery has vigorously researched

Since CuInSe₂ (CIS) based solar battery, one of the attractive solar cell materials, shows the maximum efficiency reached up to 20.9% and long life time at large scale modules, commercialization of CIS based solar battery is stimulated. However, it is also true that these cell are deposited in high vacuum condition, which lead the loss of natural resources and also energy. So, various researches were vigorously researched of chemical reduction method since it is ecological and also economical technique. Ye et al. synthesized Cu-In alloy particles by using chemical reduction method in organic solvent and the Cu-In alloy precursor films were transformed to CuInSe₂ films by selenization [1]. The resulting cells demonstrate a maximum energy conversion efficiency of 3.92 %. However, total cost of this method is not low since organic solvent should be used.

On the other hand, until now, we reported that the synthesis of uniform and well crystallized alloy nanoparticles, such as Pd₂₀Te₇ and also CuIn alloy nanoparticles by restrict controlling the homogenization of metallic complexes in the aqueous solution under room temperature [2]. 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, these Cu-In (CI) alloy precursor materials were applied to the synthesis of CIS printable solar cell.

     CI alloy nanoparticles were synthesized and size controlled by chemical reduction method under ambient conditions using metal chlorides as metal sources and sodium borohydride as a reducing agent. Dispersion of synthesized CI nanoparticles were printed onto Mo-sputtered glass substrates, and selenized at 575 ºC for 60min to form of CIS solar cells.

By obeying the calculation results and also electrochemical potential measurement, CI nanoparticles can be successfully synthesized in aqueous solution under room temperature. After selenization, CI was transformed into CuInSe₂ thin film solar cells. The CuInSe₂ thin film solar cells synthesized by this method exhibited a photovoltaic conversion efficiency of 2.3% under AM 1.5 G illumination. From the relationship between open circuit potential, short circuit current density, and fill factor, it indicated that smoothing of CIS films and improvement of the crystallinity and thickness should need to increase the solar cells properties.

This work has been supported by the Grant-in-Aid for Scientific Research (B) (No. 26281054).

 [1] Ye Seul Lim, et.,al, J. Phys. Chem. C, 2013, 117 (23), pp 11930–11940, [2] H. Takahashi et.,al, Applied Catalysis A: General 392 (2011) 80–85.