Hisato Kato, Yuki Yamamoto, Shinya Kato, Naoki Kishi, and Tetsuo Soga. “Fabrication and Evaluation of Two-Junction Carbon Thin Film Photovoltaic Devices”. Journal of Solar Energy Research Updates, vol. 5, Mar. 2018, pp.  1-7, doi:10.31875/2410-2199.2018.05.1.