Study Of Cu?In,Ga?Se₂ Photovoltaic Materials And Devices Fabricated By Continuous Sputtering

Copper indium gallium diselenide ?CuIn1-xGaxSe2, CIGS? is one of the most promising absorbing materials for high efficiency solar cells, due to its very high absorption coefficient, near optimism optical energy band gap and strong radiation resistance. Two mature techniques have performed to fabricate high quality CIGS absorber layer, including three stage co-evaporation, selenization of metallic precursors. However, three stage co-evaporation is difficult to large scale manufacturing due to its disadvantage of precise control of each individual elemental flux during the film deposition process and selenization process involved toxic Se-containing atmosphere becomes a safety and environmental concern. Radio frequency ?RF? magnetron sputtering process has many advantages, such as excellent stoichiometry transfer from the target to the substrate, potential for high deposition rates and good uniformity, making it suitable for preparing large area CIGS devices.In this thesis, CIGS absorber layers were deposited by magnetron sputtering from a quaternary compound target. The influence of sputtering parameters on composition, structure and physical properties was investigated. In₂Se₃ buffer layers were subsequently deposited by magnetron sputtering. Finally, CIGS devices were fabricated by continuous sputtering process and test. The main research contents are as follows.1. CIGS absorber layers were deposited by magnetron sputtering from a quaternary compound target. The influence of sputtering parameters, such as sputtering power, substrate temperature, working pressure and annealing process, on composition, structure and physical properties was intensively studied. It was found that CIGS thin films with different composition were deposited by changing sputtering power, the suitable sputtering power is 100 W. The morphology and composition of CIGS thin films were sensitive to substrate temperature. The suitable substate temperature is 380 degrees. The deposition rate and morphology were influenced by changing workong pressure. Phase evolution during the synthesis of CIGS film from glass/Mo/amorphous CIGS precursors was observed. The temperature for complete CIGS grain growth decreased to 150 degrees with a decrease in the size of precursors to atomic-scale. The diffusion of Ga in Cu-rich condition is easier. A liquid Cu-Se alloy formed on the surface of Cu-rich films assisted grain growth. At that point, grain size of Cu-rich films increases remarkably.2. Crystalline In₂Se₃ films were fabricated by magnetron sputtering from a sintering compound target and the effects of Indium concentration and film thickness on the phase structure, morphology and optical property were made clear. The ?-phase can persist at room temperature in the In-rich films, which is not suitable for buffer layers. The optical band gap was effected by increase of film thickness. In₂Se₃ films with thickness of under 80 nm is suitable for buffer layers.3. CIGS devices were fabricated by continuous sputtering process and test. Schottky barrier of 0.46 eV was found at Mo/CIGS interface and no power output. After aging treatment, schottky barrier disappears and the device output a little power. After 200 ? annealing treatment, open circuit voltage was up to 106 mV, short circuit current density was up to 1.10 mA/cm2, efficiency of 0.029% has been achieved without post-selenization. The results revealed that a large number of defects is the main reason for low efficiency.The continuous sputtering technology of CIGS solar cells is one kind of the whole dry process. The low efficiency could be improved in the future work. This simple, economical and non-toxic technology would be scaled up or integrated into a commercial process.