Properties of Cu(In,Ga)Se2 Thin Film Solar Cells on Ga Temperature Variation

In this paper the effect the Ga/(In+Ga) ratio, which was controlled by Ga cell temperature, on the growth behavior of Cu(In,Ga)Se2 (CIGS) thin film and its photovoltaic performance is presented. It was found that both the grain size and the void density of CIGS layer decreased due to higher incorporation of Ga in CIGS by increasing Ga temperature. It was revealed that the CIGS films satisfying the composition ratio of Ga/(In+Ga) = 0.3∼0.4 and Cu/(In+Ga) = 0.84∼1.04, which were obtained at the Ga temperature of 1033∼1035°C, has the comparable diffraction intensity of (112) and (220) peaks. The (112)/(220) peak ratio of either Cu-rich or heavily Cu-poor CIGS films was found to deviate from unity and the solar cells made at these composition range showed lower photovoltaic performances. The highest efficiency of solar cell obtained by adjusting Ga cell temperature was 8.93% on device area of 0.16 cm2 (fill factor, open circuit voltage, and short circuit current were 50.34%, 576 mV and 30.79 mA/cm2, respectiv...