Se interlayer in CIGS absorption layer for solar cell devices

• Published in: Journal of alloys and compounds 2015-06, Vol.633, p.31-36
• Main Authors: Lee, Seung-Kyu, Sim, Jae-Kwan, Kissinger, N.J. Suthan, Song, Il-Seok, Kim, Jin-Soo, Baek, Byung-Joon, Lee, Cheul-Ro
• Format: Article
• Language: English
• Subjects: Diffusion barrier; Fe diffusion; Flexible Cu(In,Ga)Se2 (CIGS); Ga gradient; Sputtering; Stainless steel
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/j.jallcom.2015.01.126

•Se interlayer is deposited between the CuGa and CuIn/In/Mo/STS stacked layer.•Both CIG precursor layers were selenized at 500°C for 1h.•SIMS depth profile shows that Ga distribution is uniform by Se interlayer.•The efficiency was improved for the CIGS solar cell by Se interlayer. A CIGS absorber layer with high gallium contents in the space-charge region can reduce the carrier recombination and improve the open circuit voltage Voc. Therefore, controlling Ga grading on top of CIGS thin film solar cells is the main objective of this experiment. To reduce Selenium (Se) vacancy, it is important that the diffusion of Ga elements into Se vacancy between Mo back contact and CIGS absorption layer would be controlled. In order to reduce Se vacancy and confirm Ga inter-diffusion, two CIGS solar cells were fabricated by converting CIG precursor with and without Se interlayer. The copper-indium metallic precursors were fabricated corresponding to the sequence CuIn/In/Mo/STS on stainless steel (STS) substrates by sequential direct current magnetron sputtering while Se layer was evaporated by rapid thermal annealing (RTA) system to obtain a Se/CuIn/In/Mo/STS stack. CuGa precursor layer was also fabricated on the Se/CuIn/In/Mo/STS stack. Finally, both CuGa/Se/CuIn/In/Mo/STS and CuGa/CuIn/In/Mo/STS stacks were selenized at 500°C for 1h. It was clearly observed from the secondary ion mass spectroscopy (SIMS) and X-ray diffraction (XRD) that there was a change between the fabricated CIGS absorption layers and the amount of Ga elements. Furthermore, the Ga elements gradually decreased from the top to the bottom layer of the CIGS absorption layer. We also discussed the effect of Se interlayer in the CIGS absorption layer and its influence on the solar cell’s performance.