Jen-Cheng Sung

Cu(In,Ga)Se 2 thin films codoped with sodium and bismuth ions for the use in the solar cells

The codoping effects of sodium and bismuth ions on the characteristics of Cu(In,Ga)Se2 films prepared via the solution process were investigated in this study. When sodium and bismuth ions were incorporated into Cu(In,Ga)Se2, the ratio of the intensity of (112) diffraction peak to that of (220/204) diffraction peak was greatly increased. The codoping process not only enlarged the sizes of the grains in the films but also resulted in densification of the films. The carrier concentration of Cu(In,Ga)Se2 was found to be effectively increased to cause a reduction in the resistivity of the films. The above phenomena were attributed to the densified microstructures of the films and a decrease in the amount of the donor-type defects. The leakage current of the solar cells was found to be also decreased via the codoping process. Owing to the improved electrical properties of Cu(In,Ga)Se2 films, the conversion efficiency of the fabricated solar cells was significantly enhanced.

Controlled orientation and improved photovoltaic characteristics of Cu(In,Ga)Se 2 solar cells via using In 2 Se 3 seeding layers

In2Se3 films were utilized as seeding layers in the synthesis of Cu(In,Ga)Se2 films via the spin-coating route. Selenizing the indium-containing precursors at 400°C resulted in the formation of the hexagonal γ-In2Se3 with the preferred (006) orientation. Increasing the selenization temperature to 500°C yielded the (300)-oriented γ-In2Se3. Using the preferred (006)-oriented In2Se3 as seeding layers produced the preferred (112)-oriented Cu(In,Ga)Se2 film because of the crystalline symmetry. In contrast, the use of the (300)- oriented In2Se3 as seeding layers yielded the (220/204)-oriented Cu(In,Ga)Se2 films. According to results obtained using SEM and the Hall effect, (112)-oriented Cu(In,Ga)Se2 films had a denser morphology and more favorable electrical properties. Using the (112)-oriented Cu(In,Ga)Se2 films as the absorber layer in the solar devices resulted in a significant increase in the conversion efficiency.