Effects of substrate temperatures in the three-stage growth of CuIn1 − xGaxSe2 thin films and their photovoltaic performances

- Three-stage growth process of CIGS on 10 cm × 10 cm substrates were investigated.
- Se flux must be over-supplied.
- Optimum values of T1 and T2 are found to be 370 °C and 520 °C, respectively.
- Higher T2 deteriorated device performances.
- High efficiency devices have higher ratio I[(112)]:I[(220)/(204)]

CuIn1 − xGaxSe2 (CIGS) polycrystalline thin film solar cells were deposited on 10 cm × 10 cm Mo-coated soda-lime glass (SLG) substrates using the three-stage co-evaporation process. The formation of (In,Ga)2Se3 precursor layer was strongly affected by the Se flux supplied during the first stage of the deposition. In our deposition system, the Se source temperature of 300 °C was sufficient for the growth of precursor and throughout the entire deposition. Then, the influence of the substrate temperatures during the first stage (T1), the second and third stages (T2) of the CIGS thin film depositions were investigated by varying T1 from 300 °C-410 °C and T2 from 500 °C-580 °C. The radiation from the surface of the growing films detected by a pyrometer and the output power of the substrate temperature controller were used to monitor the deposition process. For our system, the optimum values of T1 and T2 were 370 °C and 520 °C, respectively. The XRD results showed the highest (112):(220)/(204) intensity ratio of the chalcopyrite phase for T1 = 370 °C and T2 = 520 °C resulting in the device's maximum efficiency of 13.7%.