| 초록 |
CIGS thin films are promising materials for solar cells, as they feature a high conversion efficiency, a relatively low cost. However, a definitive understanding regarding CIGS compound has yet to be reached due to many defects or defect complexes in CIGS films, Na effect, vacancy at the CIGS surface, and Mo-Se bonding at the interface. Especially, defect such as Se vacancy at the CIGS surface can directly influence an efficiency of CIGS solar cells by a major factor of surface oxidation and it has many variables to be interpreted due to a relationship with buffer layer such as interface charge variation between buffer layer and CIGS surface, and a change of CIGS surface state itself. Therefore, the CIGS films fabricated by 3-stage co-evaporation were annealed at 200oC in Se atmosphere using closed space sublimation (CSS) system. And structural differences of standard (not anneal) and Se annealed CIGS films were investigated by SEM and Raman spectroscopy. Photoluminescence (PL) spectra of both films were measured at 10k using He-Ne ion laser with an excitation wavelength of 633nm. Different PL intensity and peak profile may be related to Cu vacancy. Surface concentration, especially Cu, was studied by x-ray photoelectron spectroscopy (XPS) measurements. This results also show a Cu removal from CIGS surface. Type- inversion at the Se annealed CIGS surface from the result of ultraviolet photoelectron spectroscopy (UPS) was confirmed. This seems to be a reason of increased open-circuit voltage and improved electrical resistance. |
