Fu-Shan Chen

Incorporation of selenium ions in solution-processed Cu(In,Ga)Se2 films

Cu(In,Ga)Se2 films were prepared on the molybdenum-coated soda-lime substrate using various processes to incorporate selenium ions. Selenium ion-containing solutions and selenium vapor were both used as the sources of selenium. When the precursors of Cu(In,Ga)Se2 were coated with selenium ion-containing solutions, the formation of MoSe2 was detected via secondary ion mass spectroscopy and GIXD analysis. The formation of thick MoSe2 films tended to retard the formation of Cu(In,Ga)Se2 and reduced the grain size of the prepared films. Therefore, the thick MoSe2 layer led to a decrease in the fill factor and the short-circuit density of the fabricated Cu(In,Ga)Se2 solar cells. The selenium ion-containing solutions were found to be easily evaporated during the heating process, thereby resulting in a decrease in the thickness and the porous microstructures of films. The decrease in the thickness of Cu(In,Ga)Se2 led to the decrease in the fill factors and the short-circuit density of the fabricated devices. The efficiency of Cu(In,Ga)Se2 solar cells prepared via selenium vapor was higher than that prepared via selenium ions. The photovoltaic characteristics of the fabricated solar cells were demonstrated to depend substantially on the routes of supplying and incorporation of selenium ions at elevated temperatures.

Preparation and characterization of Cu(In,Ga)Se2 films from nanosized alloy precursors

CuInSe2 films were successfully prepared from the nanoparticles that were synthesized via the chemical reduction reaction. In the chemical reduction process using ethylene glycol as the solvent and NaBH4 as a reducing agent, CuIn and Cu2In phases were detected. Upon increasing the molar ratio of the reducing agent to the metal ions, Cu11In9 and In were formed and coexisted with Cu–In alloys. The obtained nanoparticles were utilized in pastes for coating Cu(In,Ga)Se2 films. The XRD results and Raman spectra elucidated the formation mechanism. During the selenization process, InSe and Cu2−xSe were produced and then reacted with each other to yield CuInSe2. Cu(In,Ga)Se2 was also prepared using the nanoparticles via the reduction reaction. In the route developed herein not only was the temperature of the synthesis of the chalcopyrite compounds reduced to 450xa0°C, but also the phases of the powders that were used in the synthesis of Cu(In,Ga)Se2 films were controlled.

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.

Preparation of AgIn1−xGaxSe2 films from sol–gel derived precursors via a coating method

AgIn1−xGaxSe2 films were prepared via coating the pastes that contained sol–gel derived precursors and selenium powders, followed by the normal heating process without using H2Se. Pure-phased AgIn1−xGaxSe2 films were successfully obtained after heating in a reducing atmosphere (H2/N2) at 500xa0°C for 0.5xa0h. As the flow rate of the carrier gas was reduced, In2O3 and Ag2Se phases in the obtained films disappeared owing to prolonged residence time for selenium vapor to react with the precursors. In the paste-coating process, the gallium-ion content of the prepared films was effectively adjusted using the sol–gel route. The lattice constants of AgIn1−xGaxSe2 decreased with increasing the gallium-ion contents. The uniformity throughout AgIn1−xGaxSe2 films was confirmed by using the grazing incident X-ray diffraction analysis. The band gap energy increased nonlinearly from 1.27 to 1.63xa0eV as the molar ratio of gallium ions to IIIA ions (indium ions and gallium ions) increased from 0.2 to 0.8.