The optical and structural properties of CuIn1−x Ga x Se2 thin films fabricated with various Ga contents by using the co-evaporation technique
Tóm tắt
The purpose of the present study is to investigate the optical and the structural properties of CuIn1−x
Ga
x
Se2 (CIGS) thin films with various Ga/[In+Ga] ratios grown by using the coevaporation technique. The Ga ratios were 0, 0.15, 0.29, 0.40, 0.56, 0.73, and 1. As the Ga/[In+Ga] ratio increased, the grain size of CIGS films decreased, and the X-ray diffraction (XRD) peaks of the CIGS films progressively shifted to higher diffraction angles. In the cross-sectional scanning electron microscopy (SEM) images, the grain size of the CIGS thin films near the molybdenum electrode was smaller than it was near the CIGS surface. These results indicate that the diffusion rates of elements were different. The photocurrent (PC) spectra also showed that the band gap energy of the CIGS films increased as the Ga/[In+Ga] ratio increased. Accordingly, the short-circuit current density (J
SC
) linearly decreased, and the open-circuit voltage (V
OC
) increased and saturated at high Ga/[In+Ga] ratios (x > 0.4) due to the defects on the CIGS films surface. A correlation between the Ga/[In+Ga] ratio and the number of surface defects for the CIGS films is discussed.
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