Electrical properties of CIGS/Mo junctions as a function of MoSe2 orientation and Na doping

• Published in: Progress in photovoltaics 2014-01, Vol.22 (1), p.90-96
• Main Authors: Yoon, Ju-Heon, Kim, Jun-Ho, Kim, Won Mok, Park, Jong-Keuk, Baik, Young-Joon, Seong, Tae-Yeon, Jeong, Jeung-hyun
• Format: Article
• Language: English
• Subjects: Applied sciences; CIGS thin-film solar cells; CIGS/Mo contact resistance; Energy; Exact sciences and technology; inverse transmission line method; MoSe2 orientation; Na doping; Natural energy; Photovoltaic conversion; Solar cells. Photoelectrochemical cells; Solar energy
• ISSN: 1062-7995; 1099-159X
• DOI: 10.1002/pip.2377

ABSTRACT The electrical properties of Cu(In,Ga)Se2/Mo junctions were characterized with respect of MoSe2 orientation and Na doping level using an inverse transmission line method, in which the Cu(In,Ga)Se2 (CIGS)/Mo contact resistance could be measured separately from the CIGS film sheet resistance. The MoSe2 orientation was controlled by varying the Mo surface density, with the c‐axis parallel and normal orientations favored on Mo surfaces of lower and higher density, respectively. The effect of Na doping was compared by using samples with and without a SiOx film on sodalime glass. The conversion of the MoSe2 orientation from c‐axis normal to parallel produced a twofold reduction in CIGS/Mo contact resistance. Measurements of the contact resistances as a function of temperature showed that the difference in CIGS/Mo contact resistance between the samples with different MoSe2 orientations was due to different barrier heights at the back contact. Comparison between Na‐doped and Na‐reduced samples revealed that the contact resistance for the Na‐reduced system was four times of that of the doped sample, which showed more pronounced Schottky‐junction behavior at lower temperature, indicating that Na doping effectively reduced the barrier height at the back contact. Copyright © 2013 John Wiley & Sons, Ltd. The electrical properties of Cu(In,Ga)Se2/Mo junctions were successfully characterized in terms of contact resistance using modified (inverse) transmission line method, in which the Cu(In,Ga)Se2/Mo contact resistance could be measured separately from the CIGS film sheet resistance. The measurement showed that the substantial Na doping as well as the switching of MoSe2 structure toward c‐axis parallel orientation could reduce the barrier height at back contact, favoring higher photovoltaic conversion efficiency.