Status of Four-Junction Cell Development at Fraunhofer ISE D. Lackner, O. Höhn, A.W. Walker, M. Niemeyer, P. Beutel, G. Siefer, M. Schachtner, V. Klinger, E. Oliva, K. Hillerich et al. (4 more) E3S Web Conf., 16 (2017) 03009 Published online: 23 May 2017 DOI: 10.1051/e3sconf/20171603009