Effect of substrate temperature during the three-stage process on the CuInSe2 solar cell characteristics

CuInSe2 (CISe) with a bandgap of 1.0 eV is the appropriate bottom layer material for the multi-junction solar cell. CISe thin films have been prepared using the three-stage process, in which the substrate temperature (Ts) of the second and the third stage was varied from 490 to 580 °C. The preferred orientation of the CISe film changed from (112) to (220) as the Ts was increased from 490 °C to onward. CISe films had large and columnar grains at all values of Ts, but surface became increasingly smoother as the Ts was increased from 490 to 580 °C. Secondary ion mass spectrometry analysis revealed that Cd diffusion from CdS buffer layer to CISe layer was more when the preferred orientation was (220), which helped in the formation of homojunction inside CISe. Open circuit voltage increased upon increasing the Ts due to the increase in the Na concentration inside CISe. The conversion efficiency of the solar cells increased from 8.80 to 12.64% when the Ts was raised from 490 to 580 °C.